{ "version": "2.2", "instance": { "d54223d485bpos.htm": { "nsprefix": "nmsf", "nsuri": "http://www.northwesternmutual.com/20251231", "dts": { "inline": { "local": [ "d54223d485bpos.htm" ] }, "schema": { "local": [ "nmsf-20251231.xsd" ], "remote": [ "http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd", "http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd", "http://www.xbrl.org/2003/xl-2003-12-31.xsd", "http://www.xbrl.org/2003/xlink-2003-12-31.xsd", "http://www.xbrl.org/2005/xbrldt-2005.xsd", "http://www.xbrl.org/2006/ref-2006-02-27.xsd", "http://www.xbrl.org/lrr/arcrole/deprecated-2009-12-16.xsd", "http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd", "http://www.xbrl.org/lrr/role/net-2009-12-16.xsd", "https://www.xbrl.org/2020/extensible-enumerations-2.0.xsd", "https://www.xbrl.org/dtr/type/2020-01-21/types.xsd", "https://www.xbrl.org/dtr/type/2022-03-31/types.xsd", "https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd", "https://xbrl.fasb.org/srt/2024/elts/srt-roles-2024.xsd", "https://xbrl.fasb.org/srt/2024/elts/srt-types-2024.xsd", "https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd", "https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd", "https://xbrl.fasb.org/us-gaap/2024/elts/us-types-2024.xsd", "https://xbrl.sec.gov/country/2024/country-2024.xsd", "https://xbrl.sec.gov/country/2024/country-2024_def.xsd", "https://xbrl.sec.gov/dei/2024/dei-2024.xsd", "https://xbrl.sec.gov/oef/2024q3/oef-2024q3.xsd", "https://xbrl.sec.gov/oef/2024q3/oef-2024q3_cal.xsd", "https://xbrl.sec.gov/oef/2024q3/oef-2024q3_lab.xsd", "https://xbrl.sec.gov/oef/2024q3/oef-rr-2024q3.xsd", "https://xbrl.sec.gov/stpr/2024/stpr-2024.xsd" ] } }, "keyStandard": 59, "keyCustom": 0, "axisStandard": 4, "axisCustom": 0, "memberStandard": 7, "memberCustom": 143, "hidden": { "total": 334, "http://xbrl.sec.gov/oef/2024q3": 330, "http://xbrl.sec.gov/dei/2024": 4 }, "contextCount": 992, "entityCount": 1, "segmentCount": 150, "elementCount": 316, "unitCount": 2, "baseTaxonomies": { "http://xbrl.sec.gov/oef/2024q3": 2162, "http://xbrl.sec.gov/dei/2024": 6 }, "report": { "R1": { "role": "http://xbrl.sec.gov/rr/role/N1aCover", "longName": "010000 - Disclosure - Form N-1A Cover", "shortName": "Form N-1A Cover", "isDefault": "true", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "1", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R2": { "role": "http://www.northwesternmutual.com/10/role/N1aCover", "longName": "1010000 - Disclosure - Index 400 Stock Portfolio N-1A Cover", "shortName": "Index 400 Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "2", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R3": { "role": "http://www.northwesternmutual.com/10/role/RiskReturn", "longName": "1010001 - Disclosure - Index 400 Stock Portfolio Investment Objectives and Goals", "shortName": "Index 400 Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "3", "firstAnchor": { "contextRef": "S000000054", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R4": { "role": "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "longName": "1010002 - Disclosure - Index 400 Stock Portfolio Fees and Expenses", "shortName": "Index 400 Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "4", "firstAnchor": { "contextRef": "S000000054", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R5": { "role": "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "longName": "1010003 - Disclosure - Index 400 Stock Portfolio Investment Strategy", "shortName": "Index 400 Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "5", "firstAnchor": { "contextRef": "S000000054", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R6": { "role": "http://www.northwesternmutual.com/10/role/InvestmentRisks", "longName": "1010004 - Disclosure - Index 400 Stock Portfolio Investment Risks", "shortName": "Index 400 Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "6", "firstAnchor": { "contextRef": "S000000054_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R7": { "role": "http://www.northwesternmutual.com/10/role/PerformanceManagement", "longName": "1010005 - Disclosure - Index 400 Stock Portfolio Performance Management", "shortName": "Index 400 Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "7", "firstAnchor": { "contextRef": "S000000054", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R8": { "role": "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "longName": "1020010 - Disclosure - Index 400 Stock Portfolio Shareholder Fees", "shortName": "Index 400 Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "8", "firstAnchor": null, "uniqueAnchor": null }, "R9": { "role": "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "longName": "1020020 - Disclosure - Index 400 Stock Portfolio Annual Fund Operating Expenses", "shortName": "Index 400 Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "9", "firstAnchor": { "contextRef": "S000000054", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R10": { "role": "http://www.northwesternmutual.com/10/role/ExpenseExample", "longName": "1020030 - Disclosure - Index 400 Stock Portfolio Expense Example", "shortName": "Index 400 Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "10", "firstAnchor": { "contextRef": "S000000054_C000000089", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000054_C000000089", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R11": { "role": "http://www.northwesternmutual.com/10/role/BarChartData", "longName": "1020050 - Disclosure - Index 400 Stock Portfolio Annual Total Returns", "shortName": "Index 400 Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "11", "firstAnchor": null, "uniqueAnchor": null }, "R12": { "role": "http://www.northwesternmutual.com/10/role/PerformanceTableData", "longName": "1020060 - Disclosure - Index 400 Stock Portfolio Average Annual Total Returns", "shortName": "Index 400 Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "12", "firstAnchor": { "contextRef": "_SPMidCap400IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_SPMidCap400IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R13": { "role": "http://www.northwesternmutual.com/1/role/N1aCover", "longName": "110000 - Disclosure - Growth Stock Portfolio N-1A Cover", "shortName": "Growth Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "13", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R14": { "role": "http://www.northwesternmutual.com/1/role/RiskReturn", "longName": "110001 - Disclosure - Growth Stock Portfolio Investment Objectives and Goals", "shortName": "Growth Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "14", "firstAnchor": { "contextRef": "S000000056", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R15": { "role": "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "longName": "110002 - Disclosure - Growth Stock Portfolio Fees and Expenses", "shortName": "Growth Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "15", "firstAnchor": { "contextRef": "S000000056", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R16": { "role": "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "longName": "110003 - Disclosure - Growth Stock Portfolio Investment Strategy", "shortName": "Growth Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "16", "firstAnchor": { "contextRef": "S000000056", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R17": { "role": "http://www.northwesternmutual.com/1/role/InvestmentRisks", "longName": "110004 - Disclosure - Growth Stock Portfolio Investment Risks", "shortName": "Growth Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "17", "firstAnchor": { "contextRef": "S000000056_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R18": { "role": "http://www.northwesternmutual.com/1/role/PerformanceManagement", "longName": "110005 - Disclosure - Growth Stock Portfolio Performance Management", "shortName": "Growth Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "18", "firstAnchor": { "contextRef": "S000000056", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R19": { "role": "http://www.northwesternmutual.com/11/role/N1aCover", "longName": "1110000 - Disclosure - Mid Cap Value Portfolio N-1A Cover", "shortName": "Mid Cap Value Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "19", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R20": { "role": "http://www.northwesternmutual.com/11/role/RiskReturn", "longName": "1110001 - Disclosure - Mid Cap Value Portfolio Investment Objectives and Goals", "shortName": "Mid Cap Value Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "20", "firstAnchor": { "contextRef": "S000000053", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R21": { "role": "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "longName": "1110002 - Disclosure - Mid Cap Value Portfolio Fees and Expenses", "shortName": "Mid Cap Value Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "21", "firstAnchor": { "contextRef": "S000000053", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R22": { "role": "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "longName": "1110003 - Disclosure - Mid Cap Value Portfolio Investment Strategy", "shortName": "Mid Cap Value Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "22", "firstAnchor": { "contextRef": "S000000053", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R23": { "role": "http://www.northwesternmutual.com/11/role/InvestmentRisks", "longName": "1110004 - Disclosure - Mid Cap Value Portfolio Investment Risks", "shortName": "Mid Cap Value Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "23", "firstAnchor": { "contextRef": "S000000053_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R24": { "role": "http://www.northwesternmutual.com/11/role/PerformanceManagement", "longName": "1110005 - Disclosure - Mid Cap Value Portfolio Performance Management", "shortName": "Mid Cap Value Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "24", "firstAnchor": { "contextRef": "S000000053", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R25": { "role": "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "longName": "1120010 - Disclosure - Mid Cap Value Portfolio Shareholder Fees", "shortName": "Mid Cap Value Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "25", "firstAnchor": null, "uniqueAnchor": null }, "R26": { "role": "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "longName": "1120020 - Disclosure - Mid Cap Value Portfolio Annual Fund Operating Expenses", "shortName": "Mid Cap Value Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "26", "firstAnchor": { "contextRef": "S000000053", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R27": { "role": "http://www.northwesternmutual.com/11/role/ExpenseExample", "longName": "1120030 - Disclosure - Mid Cap Value Portfolio Expense Example", "shortName": "Mid Cap Value Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "27", "firstAnchor": { "contextRef": "S000000053_C000000088", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000053_C000000088", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R28": { "role": "http://www.northwesternmutual.com/11/role/BarChartData", "longName": "1120050 - Disclosure - Mid Cap Value Portfolio Annual Total Returns", "shortName": "Mid Cap Value Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "28", "firstAnchor": null, "uniqueAnchor": null }, "R29": { "role": "http://www.northwesternmutual.com/11/role/PerformanceTableData", "longName": "1120060 - Disclosure - Mid Cap Value Portfolio Average Annual Total Returns", "shortName": "Mid Cap Value Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "29", "firstAnchor": { "contextRef": "_RussellMidCapValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_RussellMidCapValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R30": { "role": "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "longName": "120010 - Disclosure - Growth Stock Portfolio Shareholder Fees", "shortName": "Growth Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "30", "firstAnchor": null, "uniqueAnchor": null }, "R31": { "role": "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "longName": "120020 - Disclosure - Growth Stock Portfolio Annual Fund Operating Expenses", "shortName": "Growth Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "31", "firstAnchor": { "contextRef": "S000000056", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R32": { "role": "http://www.northwesternmutual.com/1/role/ExpenseExample", "longName": "120030 - Disclosure - Growth Stock Portfolio Expense Example", "shortName": "Growth Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "32", "firstAnchor": { "contextRef": "S000000056_C000000091", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000056_C000000091", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R33": { "role": "http://www.northwesternmutual.com/1/role/BarChartData", "longName": "120050 - Disclosure - Growth Stock Portfolio Annual Total Returns", "shortName": "Growth Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "33", "firstAnchor": null, "uniqueAnchor": null }, "R34": { "role": "http://www.northwesternmutual.com/1/role/PerformanceTableData", "longName": "120060 - Disclosure - Growth Stock Portfolio Average Annual Total Returns", "shortName": "Growth Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "34", "firstAnchor": { "contextRef": "_Russell1000GrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000091_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R35": { "role": "http://www.northwesternmutual.com/12/role/N1aCover", "longName": "1210000 - Disclosure - Small Cap Growth Stock Portfolio N-1A Cover", "shortName": "Small Cap Growth Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "35", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R36": { "role": "http://www.northwesternmutual.com/12/role/RiskReturn", "longName": "1210001 - Disclosure - Small Cap Growth Stock Portfolio Investment Objectives and Goals", "shortName": "Small Cap Growth Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "36", "firstAnchor": { "contextRef": "S000000039", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R37": { "role": "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "longName": "1210002 - Disclosure - Small Cap Growth Stock Portfolio Fees and Expenses", "shortName": "Small Cap Growth Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "37", "firstAnchor": { "contextRef": "S000000039", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R38": { "role": "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "longName": "1210003 - Disclosure - Small Cap Growth Stock Portfolio Investment Strategy", "shortName": "Small Cap Growth Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "38", "firstAnchor": { "contextRef": "S000000039", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R39": { "role": "http://www.northwesternmutual.com/12/role/InvestmentRisks", "longName": "1210004 - Disclosure - Small Cap Growth Stock Portfolio Investment Risks", "shortName": "Small Cap Growth Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "39", "firstAnchor": { "contextRef": "S000000039_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R40": { "role": "http://www.northwesternmutual.com/12/role/PerformanceManagement", "longName": "1210005 - Disclosure - Small Cap Growth Stock Portfolio Performance Management", "shortName": "Small Cap Growth Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "40", "firstAnchor": { "contextRef": "S000000039", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R41": { "role": "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "longName": "1220010 - Disclosure - Small Cap Growth Stock Portfolio Shareholder Fees", "shortName": "Small Cap Growth Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "41", "firstAnchor": null, "uniqueAnchor": null }, "R42": { "role": "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "longName": "1220020 - Disclosure - Small Cap Growth Stock Portfolio Annual Fund Operating Expenses", "shortName": "Small Cap Growth Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "42", "firstAnchor": { "contextRef": "S000000039_C000000074", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039_C000000074", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R43": { "role": "http://www.northwesternmutual.com/12/role/ExpenseExample", "longName": "1220030 - Disclosure - Small Cap Growth Stock Portfolio Expense Example", "shortName": "Small Cap Growth Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "43", "firstAnchor": { "contextRef": "S000000039_C000000074", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000039_C000000074", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R44": { "role": "http://www.northwesternmutual.com/12/role/BarChartData", "longName": "1220050 - Disclosure - Small Cap Growth Stock Portfolio Annual Total Returns", "shortName": "Small Cap Growth Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "44", "firstAnchor": null, "uniqueAnchor": null }, "R45": { "role": "http://www.northwesternmutual.com/12/role/PerformanceTableData", "longName": "1220060 - Disclosure - Small Cap Growth Stock Portfolio Average Annual Total Returns", "shortName": "Small Cap Growth Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "45", "firstAnchor": { "contextRef": "_Russell2000GrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_Russell2000GrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R46": { "role": "http://www.northwesternmutual.com/13/role/N1aCover", "longName": "1310000 - Disclosure - Index 600 Stock Portfolio N-1A Cover", "shortName": "Index 600 Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "46", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R47": { "role": "http://www.northwesternmutual.com/13/role/RiskReturn", "longName": "1310001 - Disclosure - Index 600 Stock Portfolio Investment Objectives and Goals", "shortName": "Index 600 Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "47", "firstAnchor": { "contextRef": "S000018231", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R48": { "role": "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "longName": "1310002 - Disclosure - Index 600 Stock Portfolio Fees and Expenses", "shortName": "Index 600 Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "48", "firstAnchor": { "contextRef": "S000018231", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R49": { "role": "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "longName": "1310003 - Disclosure - Index 600 Stock Portfolio Investment Strategy", "shortName": "Index 600 Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "49", "firstAnchor": { "contextRef": "S000018231", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R50": { "role": "http://www.northwesternmutual.com/13/role/InvestmentRisks", "longName": "1310004 - Disclosure - Index 600 Stock Portfolio Investment Risks", "shortName": "Index 600 Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "50", "firstAnchor": { "contextRef": "S000018231_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R51": { "role": "http://www.northwesternmutual.com/13/role/PerformanceManagement", "longName": "1310005 - Disclosure - Index 600 Stock Portfolio Performance Management", "shortName": "Index 600 Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "51", "firstAnchor": { "contextRef": "S000018231", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R52": { "role": "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "longName": "1320010 - Disclosure - Index 600 Stock Portfolio Shareholder Fees", "shortName": "Index 600 Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "52", "firstAnchor": null, "uniqueAnchor": null }, "R53": { "role": "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "longName": "1320020 - Disclosure - Index 600 Stock Portfolio Annual Fund Operating Expenses", "shortName": "Index 600 Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "53", "firstAnchor": { "contextRef": "S000018231_C000050279", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231_C000050279", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R54": { "role": "http://www.northwesternmutual.com/13/role/ExpenseExample", "longName": "1320030 - Disclosure - Index 600 Stock Portfolio Expense Example", "shortName": "Index 600 Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "54", "firstAnchor": { "contextRef": "S000018231_C000050279", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018231_C000050279", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R55": { "role": "http://www.northwesternmutual.com/13/role/BarChartData", "longName": "1320050 - Disclosure - Index 600 Stock Portfolio Annual Total Returns", "shortName": "Index 600 Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "55", "firstAnchor": null, "uniqueAnchor": null }, "R56": { "role": "http://www.northwesternmutual.com/13/role/PerformanceTableData", "longName": "1320060 - Disclosure - Index 600 Stock Portfolio Average Annual Total Returns", "shortName": "Index 600 Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "56", "firstAnchor": { "contextRef": "_SPSmallCap600IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_SPSmallCap600IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R57": { "role": "http://www.northwesternmutual.com/14/role/N1aCover", "longName": "1410000 - Disclosure - Small Cap Value Portfolio N-1A Cover", "shortName": "Small Cap Value Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "57", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R58": { "role": "http://www.northwesternmutual.com/14/role/RiskReturn", "longName": "1410001 - Disclosure - Small Cap Value Portfolio Investment Objectives and Goals", "shortName": "Small Cap Value Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "58", "firstAnchor": { "contextRef": "S000000049", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R59": { "role": "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "longName": "1410002 - Disclosure - Small Cap Value Portfolio Fees and Expenses", "shortName": "Small Cap Value Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "59", "firstAnchor": { "contextRef": "S000000049", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R60": { "role": "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "longName": "1410003 - Disclosure - Small Cap Value Portfolio Investment Strategy", "shortName": "Small Cap Value Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "60", "firstAnchor": { "contextRef": "S000000049", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R61": { "role": "http://www.northwesternmutual.com/14/role/InvestmentRisks", "longName": "1410004 - Disclosure - Small Cap Value Portfolio Investment Risks", "shortName": "Small Cap Value Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "61", "firstAnchor": { "contextRef": "S000000049_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R62": { "role": "http://www.northwesternmutual.com/14/role/PerformanceManagement", "longName": "1410005 - Disclosure - Small Cap Value Portfolio Performance Management", "shortName": "Small Cap Value Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "62", "firstAnchor": { "contextRef": "S000000049", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R63": { "role": "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "longName": "1420010 - Disclosure - Small Cap Value Portfolio Shareholder Fees", "shortName": "Small Cap Value Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "63", "firstAnchor": null, "uniqueAnchor": null }, "R64": { "role": "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "longName": "1420020 - Disclosure - Small Cap Value Portfolio Annual Fund Operating Expenses", "shortName": "Small Cap Value Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "64", "firstAnchor": { "contextRef": "S000000049", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R65": { "role": "http://www.northwesternmutual.com/14/role/ExpenseExample", "longName": "1420030 - Disclosure - Small Cap Value Portfolio Expense Example", "shortName": "Small Cap Value Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "65", "firstAnchor": { "contextRef": "S000000049_C000000084", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000049_C000000084", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R66": { "role": "http://www.northwesternmutual.com/14/role/BarChartData", "longName": "1420050 - Disclosure - Small Cap Value Portfolio Annual Total Returns", "shortName": "Small Cap Value Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "66", "firstAnchor": null, "uniqueAnchor": null }, "R67": { "role": "http://www.northwesternmutual.com/14/role/PerformanceTableData", "longName": "1420060 - Disclosure - Small Cap Value Portfolio Average Annual Total Returns", "shortName": "Small Cap Value Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "67", "firstAnchor": { "contextRef": "_Russell2000ValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_Russell2000ValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R68": { "role": "http://www.northwesternmutual.com/15/role/N1aCover", "longName": "1510000 - Disclosure - International Growth Portfolio N-1A Cover", "shortName": "International Growth Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "68", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R69": { "role": "http://www.northwesternmutual.com/15/role/RiskReturn", "longName": "1510001 - Disclosure - International Growth Portfolio Investment Objectives and Goals", "shortName": "International Growth Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "69", "firstAnchor": { "contextRef": "S000000051", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R70": { "role": "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "longName": "1510002 - Disclosure - International Growth Portfolio Fees and Expenses", "shortName": "International Growth Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "70", "firstAnchor": { "contextRef": "S000000051", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R71": { "role": "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "longName": "1510003 - Disclosure - International Growth Portfolio Investment Strategy", "shortName": "International Growth Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "71", "firstAnchor": { "contextRef": "S000000051", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R72": { "role": "http://www.northwesternmutual.com/15/role/InvestmentRisks", "longName": "1510004 - Disclosure - International Growth Portfolio Investment Risks", "shortName": "International Growth Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "72", "firstAnchor": { "contextRef": "S000000051_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R73": { "role": "http://www.northwesternmutual.com/15/role/PerformanceManagement", "longName": "1510005 - Disclosure - International Growth Portfolio Performance Management", "shortName": "International Growth Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "73", "firstAnchor": { "contextRef": "S000000051", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R74": { "role": "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "longName": "1520010 - Disclosure - International Growth Portfolio Shareholder Fees", "shortName": "International Growth Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "74", "firstAnchor": null, "uniqueAnchor": null }, "R75": { "role": "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "longName": "1520020 - Disclosure - International Growth Portfolio Annual Fund Operating Expenses", "shortName": "International Growth Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "75", "firstAnchor": { "contextRef": "S000000051", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R76": { "role": "http://www.northwesternmutual.com/15/role/ExpenseExample", "longName": "1520030 - Disclosure - International Growth Portfolio Expense Example", "shortName": "International Growth Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "76", "firstAnchor": { "contextRef": "S000000051_C000000086", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000051_C000000086", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R77": { "role": "http://www.northwesternmutual.com/15/role/BarChartData", "longName": "1520050 - Disclosure - International Growth Portfolio Annual Total Returns", "shortName": "International Growth Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "77", "firstAnchor": null, "uniqueAnchor": null }, "R78": { "role": "http://www.northwesternmutual.com/15/role/PerformanceTableData", "longName": "1520060 - Disclosure - International Growth Portfolio Average Annual Total Returns", "shortName": "International Growth Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "78", "firstAnchor": { "contextRef": "_MSCIEAFEGrowthIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_MSCIEAFEGrowthIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R79": { "role": "http://www.northwesternmutual.com/16/role/N1aCover", "longName": "1610000 - Disclosure - Research International Core Portfolio N-1A Cover", "shortName": "Research International Core Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "79", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R80": { "role": "http://www.northwesternmutual.com/16/role/RiskReturn", "longName": "1610001 - Disclosure - Research International Core Portfolio Investment Objectives and Goals", "shortName": "Research International Core Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "80", "firstAnchor": { "contextRef": "S000018230", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R81": { "role": "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "longName": "1610002 - Disclosure - Research International Core Portfolio Fees and Expenses", "shortName": "Research International Core Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "81", "firstAnchor": { "contextRef": "S000018230", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R82": { "role": "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "longName": "1610003 - Disclosure - Research International Core Portfolio Investment Strategy", "shortName": "Research International Core Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "82", "firstAnchor": { "contextRef": "S000018230", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R83": { "role": "http://www.northwesternmutual.com/16/role/InvestmentRisks", "longName": "1610004 - Disclosure - Research International Core Portfolio Investment Risks", "shortName": "Research International Core Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "83", "firstAnchor": { "contextRef": "S000018230_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R84": { "role": "http://www.northwesternmutual.com/16/role/PerformanceManagement", "longName": "1610005 - Disclosure - Research International Core Portfolio Performance Management", "shortName": "Research International Core Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "84", "firstAnchor": { "contextRef": "S000018230", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R85": { "role": "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "longName": "1620010 - Disclosure - Research International Core Portfolio Shareholder Fees", "shortName": "Research International Core Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "85", "firstAnchor": null, "uniqueAnchor": null }, "R86": { "role": "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "longName": "1620020 - Disclosure - Research International Core Portfolio Annual Fund Operating Expenses", "shortName": "Research International Core Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "86", "firstAnchor": { "contextRef": "S000018230", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R87": { "role": "http://www.northwesternmutual.com/16/role/ExpenseExample", "longName": "1620030 - Disclosure - Research International Core Portfolio Expense Example", "shortName": "Research International Core Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "87", "firstAnchor": { "contextRef": "S000018230_C000050278", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018230_C000050278", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R88": { "role": "http://www.northwesternmutual.com/16/role/BarChartData", "longName": "1620050 - Disclosure - Research International Core Portfolio Annual Total Returns", "shortName": "Research International Core Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "88", "firstAnchor": null, "uniqueAnchor": null }, "R89": { "role": "http://www.northwesternmutual.com/16/role/PerformanceTableData", "longName": "1620060 - Disclosure - Research International Core Portfolio Average Annual Total Returns", "shortName": "Research International Core Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "89", "firstAnchor": { "contextRef": "_MSCIEAFEIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_MSCIEAFEIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R90": { "role": "http://www.northwesternmutual.com/17/role/N1aCover", "longName": "1710000 - Disclosure - International Equity Portfolio N-1A Cover", "shortName": "International Equity Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "90", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R91": { "role": "http://www.northwesternmutual.com/17/role/RiskReturn", "longName": "1710001 - Disclosure - International Equity Portfolio Investment Objectives and Goals", "shortName": "International Equity Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "91", "firstAnchor": { "contextRef": "S000000052", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R92": { "role": "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "longName": "1710002 - Disclosure - International Equity Portfolio Fees and Expenses", "shortName": "International Equity Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "92", "firstAnchor": { "contextRef": "S000000052", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R93": { "role": "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "longName": "1710003 - Disclosure - International Equity Portfolio Investment Strategy", "shortName": "International Equity Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "93", "firstAnchor": { "contextRef": "S000000052", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R94": { "role": "http://www.northwesternmutual.com/17/role/InvestmentRisks", "longName": "1710004 - Disclosure - International Equity Portfolio Investment Risks", "shortName": "International Equity Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "94", "firstAnchor": { "contextRef": "S000000052_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R95": { "role": "http://www.northwesternmutual.com/17/role/PerformanceManagement", "longName": "1710005 - Disclosure - International Equity Portfolio Performance Management", "shortName": "International Equity Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "95", "firstAnchor": { "contextRef": "S000000052", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R96": { "role": "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "longName": "1720010 - Disclosure - International Equity Portfolio Shareholder Fees", "shortName": "International Equity Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "96", "firstAnchor": null, "uniqueAnchor": null }, "R97": { "role": "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "longName": "1720020 - Disclosure - International Equity Portfolio Annual Fund Operating Expenses", "shortName": "International Equity Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "97", "firstAnchor": { "contextRef": "S000000052", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R98": { "role": "http://www.northwesternmutual.com/17/role/ExpenseExample", "longName": "1720030 - Disclosure - International Equity Portfolio Expense Example", "shortName": "International Equity Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "98", "firstAnchor": { "contextRef": "S000000052_C000000087", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000052_C000000087", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R99": { "role": "http://www.northwesternmutual.com/17/role/BarChartData", "longName": "1720050 - Disclosure - International Equity Portfolio Annual Total Returns", "shortName": "International Equity Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "99", "firstAnchor": null, "uniqueAnchor": null }, "R100": { "role": "http://www.northwesternmutual.com/17/role/PerformanceTableData", "longName": "1720060 - Disclosure - International Equity Portfolio Average Annual Total Returns", "shortName": "International Equity Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "100", "firstAnchor": { "contextRef": "_MSCIAllCountryWorldexUSValueIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_MSCIAllCountryWorldexUSValueIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R101": { "role": "http://www.northwesternmutual.com/18/role/N1aCover", "longName": "1810000 - Disclosure - Emerging Markets Equity Portfolio N-1A Cover", "shortName": "Emerging Markets Equity Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "101", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R102": { "role": "http://www.northwesternmutual.com/18/role/RiskReturn", "longName": "1810001 - Disclosure - Emerging Markets Equity Portfolio Investment Objectives and Goals", "shortName": "Emerging Markets Equity Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "102", "firstAnchor": { "contextRef": "S000018232", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R103": { "role": "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "longName": "1810002 - Disclosure - Emerging Markets Equity Portfolio Fees and Expenses", "shortName": "Emerging Markets Equity Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "103", "firstAnchor": { "contextRef": "S000018232", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R104": { "role": "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "longName": "1810003 - Disclosure - Emerging Markets Equity Portfolio Investment Strategy", "shortName": "Emerging Markets Equity Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "104", "firstAnchor": { "contextRef": "S000018232", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R105": { "role": "http://www.northwesternmutual.com/18/role/InvestmentRisks", "longName": "1810004 - Disclosure - Emerging Markets Equity Portfolio Investment Risks", "shortName": "Emerging Markets Equity Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "105", "firstAnchor": { "contextRef": "S000018232_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R106": { "role": "http://www.northwesternmutual.com/18/role/PerformanceManagement", "longName": "1810005 - Disclosure - Emerging Markets Equity Portfolio Performance Management", "shortName": "Emerging Markets Equity Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "106", "firstAnchor": { "contextRef": "S000018232", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R107": { "role": "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "longName": "1820010 - Disclosure - Emerging Markets Equity Portfolio Shareholder Fees", "shortName": "Emerging Markets Equity Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "107", "firstAnchor": null, "uniqueAnchor": null }, "R108": { "role": "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "longName": "1820020 - Disclosure - Emerging Markets Equity Portfolio Annual Fund Operating Expenses", "shortName": "Emerging Markets Equity Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "108", "firstAnchor": { "contextRef": "S000018232", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R109": { "role": "http://www.northwesternmutual.com/18/role/ExpenseExample", "longName": "1820030 - Disclosure - Emerging Markets Equity Portfolio Expense Example", "shortName": "Emerging Markets Equity Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "109", "firstAnchor": { "contextRef": "S000018232_C000050280", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018232_C000050280", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R110": { "role": "http://www.northwesternmutual.com/18/role/BarChartData", "longName": "1820050 - Disclosure - Emerging Markets Equity Portfolio Annual Total Returns", "shortName": "Emerging Markets Equity Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "110", "firstAnchor": null, "uniqueAnchor": null }, "R111": { "role": "http://www.northwesternmutual.com/18/role/PerformanceTableData", "longName": "1820060 - Disclosure - Emerging Markets Equity Portfolio Average Annual Total Returns", "shortName": "Emerging Markets Equity Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "111", "firstAnchor": { "contextRef": "_MSCIEmergingMarketsIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_MSCIEmergingMarketsIndexNetMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R112": { "role": "http://www.northwesternmutual.com/19/role/N1aCover", "longName": "1910000 - Disclosure - Government Money Market Portfolio N-1A Cover", "shortName": "Government Money Market Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "112", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R113": { "role": "http://www.northwesternmutual.com/19/role/RiskReturn", "longName": "1910001 - Disclosure - Government Money Market Portfolio Investment Objectives and Goals", "shortName": "Government Money Market Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "113", "firstAnchor": { "contextRef": "S000000048", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R114": { "role": "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "longName": "1910002 - Disclosure - Government Money Market Portfolio Fees and Expenses", "shortName": "Government Money Market Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "114", "firstAnchor": { "contextRef": "S000000048", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R115": { "role": "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "longName": "1910003 - Disclosure - Government Money Market Portfolio Investment Strategy", "shortName": "Government Money Market Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "115", "firstAnchor": { "contextRef": "S000000048", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R116": { "role": "http://www.northwesternmutual.com/19/role/InvestmentRisks", "longName": "1910004 - Disclosure - Government Money Market Portfolio Investment Risks", "shortName": "Government Money Market Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "116", "firstAnchor": { "contextRef": "S000000048_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R117": { "role": "http://www.northwesternmutual.com/19/role/PerformanceManagement", "longName": "1910005 - Disclosure - Government Money Market Portfolio Performance Management", "shortName": "Government Money Market Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "117", "firstAnchor": { "contextRef": "S000000048", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R118": { "role": "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "longName": "1920010 - Disclosure - Government Money Market Portfolio Shareholder Fees", "shortName": "Government Money Market Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "118", "firstAnchor": null, "uniqueAnchor": null }, "R119": { "role": "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "longName": "1920020 - Disclosure - Government Money Market Portfolio Annual Fund Operating Expenses", "shortName": "Government Money Market Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "119", "firstAnchor": { "contextRef": "S000000048_C000000083", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048_C000000083", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R120": { "role": "http://www.northwesternmutual.com/19/role/ExpenseExample", "longName": "1920030 - Disclosure - Government Money Market Portfolio Expense Example", "shortName": "Government Money Market Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "120", "firstAnchor": { "contextRef": "S000000048_C000000083", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000048_C000000083", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R121": { "role": "http://www.northwesternmutual.com/19/role/BarChartData", "longName": "1920050 - Disclosure - Government Money Market Portfolio Annual Total Returns", "shortName": "Government Money Market Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "121", "firstAnchor": null, "uniqueAnchor": null }, "R122": { "role": "http://www.northwesternmutual.com/19/role/PerformanceTableData", "longName": "1920060 - Disclosure - Government Money Market Portfolio Average Annual Total Returns", "shortName": "Government Money Market Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "122", "firstAnchor": { "contextRef": "C000000083_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "C000000083_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R123": { "role": "http://www.northwesternmutual.com/20/role/N1aCover", "longName": "2010000 - Disclosure - Short-Term Bond Portfolio N-1A Cover", "shortName": "Short-Term Bond Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "123", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R124": { "role": "http://www.northwesternmutual.com/20/role/RiskReturn", "longName": "2010001 - Disclosure - Short-Term Bond Portfolio Investment Objectives and Goals", "shortName": "Short-Term Bond Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "124", "firstAnchor": { "contextRef": "S000018233", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R125": { "role": "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "longName": "2010002 - Disclosure - Short-Term Bond Portfolio Fees and Expenses", "shortName": "Short-Term Bond Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "125", "firstAnchor": { "contextRef": "S000018233", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R126": { "role": "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "longName": "2010003 - Disclosure - Short-Term Bond Portfolio Investment Strategy", "shortName": "Short-Term Bond Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "126", "firstAnchor": { "contextRef": "S000018233", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R127": { "role": "http://www.northwesternmutual.com/20/role/InvestmentRisks", "longName": "2010004 - Disclosure - Short-Term Bond Portfolio Investment Risks", "shortName": "Short-Term Bond Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "127", "firstAnchor": { "contextRef": "S000018233_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R128": { "role": "http://www.northwesternmutual.com/20/role/PerformanceManagement", "longName": "2010005 - Disclosure - Short-Term Bond Portfolio Performance Management", "shortName": "Short-Term Bond Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "128", "firstAnchor": { "contextRef": "S000018233", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R129": { "role": "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "longName": "2020010 - Disclosure - Short-Term Bond Portfolio Shareholder Fees", "shortName": "Short-Term Bond Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "129", "firstAnchor": null, "uniqueAnchor": null }, "R130": { "role": "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "longName": "2020020 - Disclosure - Short-Term Bond Portfolio Annual Fund Operating Expenses", "shortName": "Short-Term Bond Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "130", "firstAnchor": { "contextRef": "S000018233_C000050281", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233_C000050281", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R131": { "role": "http://www.northwesternmutual.com/20/role/ExpenseExample", "longName": "2020030 - Disclosure - Short-Term Bond Portfolio Expense Example", "shortName": "Short-Term Bond Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "131", "firstAnchor": { "contextRef": "S000018233_C000050281", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018233_C000050281", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R132": { "role": "http://www.northwesternmutual.com/20/role/BarChartData", "longName": "2020050 - Disclosure - Short-Term Bond Portfolio Annual Total Returns", "shortName": "Short-Term Bond Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "132", "firstAnchor": null, "uniqueAnchor": null }, "R133": { "role": "http://www.northwesternmutual.com/20/role/PerformanceTableData", "longName": "2020060 - Disclosure - Short-Term Bond Portfolio Average Annual Total Returns", "shortName": "Short-Term Bond Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "133", "firstAnchor": { "contextRef": "_Bloomberg13YrUSGovtCreditBondIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_Bloomberg13YrUSGovtCreditBondIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R134": { "role": "http://www.northwesternmutual.com/2/role/N1aCover", "longName": "210000 - Disclosure - Focused Appreciation Portfolio N-1A Cover", "shortName": "Focused Appreciation Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "134", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R135": { "role": "http://www.northwesternmutual.com/2/role/RiskReturn", "longName": "210001 - Disclosure - Focused Appreciation Portfolio Investment Objectives and Goals", "shortName": "Focused Appreciation Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "135", "firstAnchor": { "contextRef": "S000000055", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R136": { "role": "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "longName": "210002 - Disclosure - Focused Appreciation Portfolio Fees and Expenses", "shortName": "Focused Appreciation Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "136", "firstAnchor": { "contextRef": "S000000055", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R137": { "role": "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "longName": "210003 - Disclosure - Focused Appreciation Portfolio Investment Strategy", "shortName": "Focused Appreciation Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "137", "firstAnchor": { "contextRef": "S000000055", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R138": { "role": "http://www.northwesternmutual.com/2/role/InvestmentRisks", "longName": "210004 - Disclosure - Focused Appreciation Portfolio Investment Risks", "shortName": "Focused Appreciation Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "138", "firstAnchor": { "contextRef": "S000000055_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R139": { "role": "http://www.northwesternmutual.com/2/role/PerformanceManagement", "longName": "210005 - Disclosure - Focused Appreciation Portfolio Performance Management", "shortName": "Focused Appreciation Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "139", "firstAnchor": { "contextRef": "S000000055", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R140": { "role": "http://www.northwesternmutual.com/21/role/N1aCover", "longName": "2110000 - Disclosure - Select Bond Portfolio N-1A Cover", "shortName": "Select Bond Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "140", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R141": { "role": "http://www.northwesternmutual.com/21/role/RiskReturn", "longName": "2110001 - Disclosure - Select Bond Portfolio Investment Objectives and Goals", "shortName": "Select Bond Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "141", "firstAnchor": { "contextRef": "S000000047", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R142": { "role": "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "longName": "2110002 - Disclosure - Select Bond Portfolio Fees and Expenses", "shortName": "Select Bond Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "142", "firstAnchor": { "contextRef": "S000000047", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R143": { "role": "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "longName": "2110003 - Disclosure - Select Bond Portfolio Investment Strategy", "shortName": "Select Bond Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "143", "firstAnchor": { "contextRef": "S000000047", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R144": { "role": "http://www.northwesternmutual.com/21/role/InvestmentRisks", "longName": "2110004 - Disclosure - Select Bond Portfolio Investment Risks", "shortName": "Select Bond Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "144", "firstAnchor": { "contextRef": "S000000047_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R145": { "role": "http://www.northwesternmutual.com/21/role/PerformanceManagement", "longName": "2110005 - Disclosure - Select Bond Portfolio Performance Management", "shortName": "Select Bond Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "145", "firstAnchor": { "contextRef": "S000000047", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R146": { "role": "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "longName": "2120010 - Disclosure - Select Bond Portfolio Shareholder Fees", "shortName": "Select Bond Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "146", "firstAnchor": null, "uniqueAnchor": null }, "R147": { "role": "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "longName": "2120020 - Disclosure - Select Bond Portfolio Annual Fund Operating Expenses", "shortName": "Select Bond Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "147", "firstAnchor": { "contextRef": "S000000047", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R148": { "role": "http://www.northwesternmutual.com/21/role/ExpenseExample", "longName": "2120030 - Disclosure - Select Bond Portfolio Expense Example", "shortName": "Select Bond Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "148", "firstAnchor": { "contextRef": "S000000047_C000000082", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000047_C000000082", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R149": { "role": "http://www.northwesternmutual.com/21/role/BarChartData", "longName": "2120050 - Disclosure - Select Bond Portfolio Annual Total Returns", "shortName": "Select Bond Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "149", "firstAnchor": null, "uniqueAnchor": null }, "R150": { "role": "http://www.northwesternmutual.com/21/role/PerformanceTableData", "longName": "2120060 - Disclosure - Select Bond Portfolio Average Annual Total Returns", "shortName": "Select Bond Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "150", "firstAnchor": { "contextRef": "_BloombergUSAggregateBondIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000082_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R151": { "role": "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "longName": "220010 - Disclosure - Focused Appreciation Portfolio Shareholder Fees", "shortName": "Focused Appreciation Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "151", "firstAnchor": null, "uniqueAnchor": null }, "R152": { "role": "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "longName": "220020 - Disclosure - Focused Appreciation Portfolio Annual Fund Operating Expenses", "shortName": "Focused Appreciation Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "152", "firstAnchor": { "contextRef": "S000000055", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R153": { "role": "http://www.northwesternmutual.com/2/role/ExpenseExample", "longName": "220030 - Disclosure - Focused Appreciation Portfolio Expense Example", "shortName": "Focused Appreciation Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "153", "firstAnchor": { "contextRef": "S000000055_C000000090", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000055_C000000090", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R154": { "role": "http://www.northwesternmutual.com/2/role/BarChartData", "longName": "220050 - Disclosure - Focused Appreciation Portfolio Annual Total Returns", "shortName": "Focused Appreciation Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "154", "firstAnchor": null, "uniqueAnchor": null }, "R155": { "role": "http://www.northwesternmutual.com/2/role/PerformanceTableData", "longName": "220060 - Disclosure - Focused Appreciation Portfolio Average Annual Total Returns", "shortName": "Focused Appreciation Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "155", "firstAnchor": { "contextRef": "_Russell1000GrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000090_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R156": { "role": "http://www.northwesternmutual.com/22/role/N1aCover", "longName": "2210000 - Disclosure - Long-Term US Government Bond Portfolio N-1A Cover", "shortName": "Long-Term US Government Bond Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "156", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R157": { "role": "http://www.northwesternmutual.com/22/role/RiskReturn", "longName": "2210001 - Disclosure - Long-Term US Government Bond Portfolio Investment Objectives and Goals", "shortName": "Long-Term US Government Bond Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "157", "firstAnchor": { "contextRef": "S000018234", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R158": { "role": "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "longName": "2210002 - Disclosure - Long-Term US Government Bond Portfolio Fees and Expenses", "shortName": "Long-Term US Government Bond Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "158", "firstAnchor": { "contextRef": "S000018234", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R159": { "role": "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "longName": "2210003 - Disclosure - Long-Term US Government Bond Portfolio Investment Strategy", "shortName": "Long-Term US Government Bond Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "159", "firstAnchor": { "contextRef": "S000018234", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R160": { "role": "http://www.northwesternmutual.com/22/role/InvestmentRisks", "longName": "2210004 - Disclosure - Long-Term US Government Bond Portfolio Investment Risks", "shortName": "Long-Term US Government Bond Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "160", "firstAnchor": { "contextRef": "S000018234_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R161": { "role": "http://www.northwesternmutual.com/22/role/PerformanceManagement", "longName": "2210005 - Disclosure - Long-Term US Government Bond Portfolio Performance Management", "shortName": "Long-Term US Government Bond Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "161", "firstAnchor": { "contextRef": "S000018234", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R162": { "role": "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "longName": "2220010 - Disclosure - Long-Term US Government Bond Portfolio Shareholder Fees", "shortName": "Long-Term US Government Bond Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "162", "firstAnchor": null, "uniqueAnchor": null }, "R163": { "role": "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "longName": "2220020 - Disclosure - Long-Term US Government Bond Portfolio Annual Fund Operating Expenses", "shortName": "Long-Term US Government Bond Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "163", "firstAnchor": { "contextRef": "S000018234", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R164": { "role": "http://www.northwesternmutual.com/22/role/ExpenseExample", "longName": "2220030 - Disclosure - Long-Term US Government Bond Portfolio Expense Example", "shortName": "Long-Term US Government Bond Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "164", "firstAnchor": { "contextRef": "S000018234_C000050282", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018234_C000050282", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R165": { "role": "http://www.northwesternmutual.com/22/role/BarChartData", "longName": "2220050 - Disclosure - Long-Term US Government Bond Portfolio Annual Total Returns", "shortName": "Long-Term US Government Bond Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "165", "firstAnchor": null, "uniqueAnchor": null }, "R166": { "role": "http://www.northwesternmutual.com/22/role/PerformanceTableData", "longName": "2220060 - Disclosure - Long-Term US Government Bond Portfolio Average Annual Total Returns", "shortName": "Long-Term US Government Bond Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "166", "firstAnchor": { "contextRef": "_BloombergLongTermTreasuryIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_BloombergLongTermTreasuryIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R167": { "role": "http://www.northwesternmutual.com/23/role/N1aCover", "longName": "2310000 - Disclosure - Inflation Managed Portfolio N-1A Cover", "shortName": "Inflation Managed Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "167", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R168": { "role": "http://www.northwesternmutual.com/23/role/RiskReturn", "longName": "2310001 - Disclosure - Inflation Managed Portfolio Investment Objectives and Goals", "shortName": "Inflation Managed Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "168", "firstAnchor": { "contextRef": "S000018228", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R169": { "role": "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "longName": "2310002 - Disclosure - Inflation Managed Portfolio Fees and Expenses", "shortName": "Inflation Managed Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "169", "firstAnchor": { "contextRef": "S000018228", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R170": { "role": "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "longName": "2310003 - Disclosure - Inflation Managed Portfolio Investment Strategy", "shortName": "Inflation Managed Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "170", "firstAnchor": { "contextRef": "S000018228", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R171": { "role": "http://www.northwesternmutual.com/23/role/InvestmentRisks", "longName": "2310004 - Disclosure - Inflation Managed Portfolio Investment Risks", "shortName": "Inflation Managed Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "171", "firstAnchor": { "contextRef": "S000018228_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R172": { "role": "http://www.northwesternmutual.com/23/role/PerformanceManagement", "longName": "2310005 - Disclosure - Inflation Managed Portfolio Performance Management", "shortName": "Inflation Managed Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "172", "firstAnchor": { "contextRef": "S000018228", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R173": { "role": "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "longName": "2320010 - Disclosure - Inflation Managed Portfolio Shareholder Fees", "shortName": "Inflation Managed Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "173", "firstAnchor": null, "uniqueAnchor": null }, "R174": { "role": "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "longName": "2320020 - Disclosure - Inflation Managed Portfolio Annual Fund Operating Expenses", "shortName": "Inflation Managed Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "174", "firstAnchor": { "contextRef": "S000018228", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R175": { "role": "http://www.northwesternmutual.com/23/role/ExpenseExample", "longName": "2320030 - Disclosure - Inflation Managed Portfolio Expense Example", "shortName": "Inflation Managed Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "175", "firstAnchor": { "contextRef": "S000018228_C000050276", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018228_C000050276", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R176": { "role": "http://www.northwesternmutual.com/23/role/BarChartData", "longName": "2320050 - Disclosure - Inflation Managed Portfolio Annual Total Returns", "shortName": "Inflation Managed Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "176", "firstAnchor": null, "uniqueAnchor": null }, "R177": { "role": "http://www.northwesternmutual.com/23/role/PerformanceTableData", "longName": "2320060 - Disclosure - Inflation Managed Portfolio Average Annual Total Returns", "shortName": "Inflation Managed Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "177", "firstAnchor": { "contextRef": "_BloombergUSTreasuryInflationProtectedSecuritiesTIPSIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_BloombergUSTreasuryInflationProtectedSecuritiesTIPSIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R178": { "role": "http://www.northwesternmutual.com/24/role/N1aCover", "longName": "2410000 - Disclosure - High Yield Bond Portfolio N-1A Cover", "shortName": "High Yield Bond Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "178", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R179": { "role": "http://www.northwesternmutual.com/24/role/RiskReturn", "longName": "2410001 - Disclosure - High Yield Bond Portfolio Investment Objectives and Goals", "shortName": "High Yield Bond Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "179", "firstAnchor": { "contextRef": "S000000046", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R180": { "role": "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "longName": "2410002 - Disclosure - High Yield Bond Portfolio Fees and Expenses", "shortName": "High Yield Bond Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "180", "firstAnchor": { "contextRef": "S000000046", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R181": { "role": "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "longName": "2410003 - Disclosure - High Yield Bond Portfolio Investment Strategy", "shortName": "High Yield Bond Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "181", "firstAnchor": { "contextRef": "S000000046", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R182": { "role": "http://www.northwesternmutual.com/24/role/InvestmentRisks", "longName": "2410004 - Disclosure - High Yield Bond Portfolio Investment Risks", "shortName": "High Yield Bond Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "182", "firstAnchor": { "contextRef": "S000000046_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R183": { "role": "http://www.northwesternmutual.com/24/role/PerformanceManagement", "longName": "2410005 - Disclosure - High Yield Bond Portfolio Performance Management", "shortName": "High Yield Bond Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "183", "firstAnchor": { "contextRef": "S000000046", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R184": { "role": "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "longName": "2420010 - Disclosure - High Yield Bond Portfolio Shareholder Fees", "shortName": "High Yield Bond Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "184", "firstAnchor": null, "uniqueAnchor": null }, "R185": { "role": "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "longName": "2420020 - Disclosure - High Yield Bond Portfolio Annual Fund Operating Expenses", "shortName": "High Yield Bond Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "185", "firstAnchor": { "contextRef": "S000000046_C000000081", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046_C000000081", "name": "oef:ManagementFeesOverAssets", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R186": { "role": "http://www.northwesternmutual.com/24/role/ExpenseExample", "longName": "2420030 - Disclosure - High Yield Bond Portfolio Expense Example", "shortName": "High Yield Bond Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "186", "firstAnchor": { "contextRef": "S000000046_C000000081", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000046_C000000081", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R187": { "role": "http://www.northwesternmutual.com/24/role/BarChartData", "longName": "2420050 - Disclosure - High Yield Bond Portfolio Annual Total Returns", "shortName": "High Yield Bond Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "187", "firstAnchor": null, "uniqueAnchor": null }, "R188": { "role": "http://www.northwesternmutual.com/24/role/PerformanceTableData", "longName": "2420060 - Disclosure - High Yield Bond Portfolio Average Annual Total Returns", "shortName": "High Yield Bond Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "188", "firstAnchor": { "contextRef": "_BloombergUSCorporateHighYield2PercentIssuerCappedIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_BloombergUSCorporateHighYield2PercentIssuerCappedIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R189": { "role": "http://www.northwesternmutual.com/25/role/N1aCover", "longName": "2510000 - Disclosure - Multi-Sector Bond Portfolio N-1A Cover", "shortName": "Multi-Sector Bond Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "189", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R190": { "role": "http://www.northwesternmutual.com/25/role/RiskReturn", "longName": "2510001 - Disclosure - Multi-Sector Bond Portfolio Investment Objectives and Goals", "shortName": "Multi-Sector Bond Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "190", "firstAnchor": { "contextRef": "S000018235", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R191": { "role": "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "longName": "2510002 - Disclosure - Multi-Sector Bond Portfolio Fees and Expenses", "shortName": "Multi-Sector Bond Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "191", "firstAnchor": { "contextRef": "S000018235", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R192": { "role": "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "longName": "2510003 - Disclosure - Multi-Sector Bond Portfolio Investment Strategy", "shortName": "Multi-Sector Bond Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "192", "firstAnchor": { "contextRef": "S000018235", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R193": { "role": "http://www.northwesternmutual.com/25/role/InvestmentRisks", "longName": "2510004 - Disclosure - Multi-Sector Bond Portfolio Investment Risks", "shortName": "Multi-Sector Bond Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "193", "firstAnchor": { "contextRef": "S000018235_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R194": { "role": "http://www.northwesternmutual.com/25/role/PerformanceManagement", "longName": "2510005 - Disclosure - Multi-Sector Bond Portfolio Performance Management", "shortName": "Multi-Sector Bond Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "194", "firstAnchor": { "contextRef": "S000018235", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R195": { "role": "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "longName": "2520010 - Disclosure - Multi-Sector Bond Portfolio Shareholder Fees", "shortName": "Multi-Sector Bond Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "195", "firstAnchor": null, "uniqueAnchor": null }, "R196": { "role": "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "longName": "2520020 - Disclosure - Multi-Sector Bond Portfolio Annual Fund Operating Expenses", "shortName": "Multi-Sector Bond Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "196", "firstAnchor": { "contextRef": "S000018235", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R197": { "role": "http://www.northwesternmutual.com/25/role/ExpenseExample", "longName": "2520030 - Disclosure - Multi-Sector Bond Portfolio Expense Example", "shortName": "Multi-Sector Bond Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "197", "firstAnchor": { "contextRef": "S000018235_C000050283", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018235_C000050283", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R198": { "role": "http://www.northwesternmutual.com/25/role/BarChartData", "longName": "2520050 - Disclosure - Multi-Sector Bond Portfolio Annual Total Returns", "shortName": "Multi-Sector Bond Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "198", "firstAnchor": null, "uniqueAnchor": null }, "R199": { "role": "http://www.northwesternmutual.com/25/role/PerformanceTableData", "longName": "2520060 - Disclosure - Multi-Sector Bond Portfolio Average Annual Total Returns", "shortName": "Multi-Sector Bond Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "199", "firstAnchor": { "contextRef": "_OneThirdEachThreeIndexesMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_OneThirdEachThreeIndexesMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R200": { "role": "http://www.northwesternmutual.com/26/role/N1aCover", "longName": "2610000 - Disclosure - Active Passive Very Aggressive Portfolio N-1A Cover", "shortName": "Active Passive Very Aggressive Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "200", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R201": { "role": "http://www.northwesternmutual.com/26/role/RiskReturn", "longName": "2610001 - Disclosure - Active Passive Very Aggressive Portfolio Investment Objectives and Goals", "shortName": "Active Passive Very Aggressive Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "201", "firstAnchor": { "contextRef": "S000091984", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R202": { "role": "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "longName": "2610002 - Disclosure - Active Passive Very Aggressive Portfolio Fees and Expenses", "shortName": "Active Passive Very Aggressive Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "202", "firstAnchor": { "contextRef": "S000091984", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R203": { "role": "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "longName": "2610003 - Disclosure - Active Passive Very Aggressive Portfolio Investment Strategy", "shortName": "Active Passive Very Aggressive Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "203", "firstAnchor": { "contextRef": "S000091984", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R204": { "role": "http://www.northwesternmutual.com/26/role/InvestmentRisks", "longName": "2610004 - Disclosure - Active Passive Very Aggressive Portfolio Investment Risks", "shortName": "Active Passive Very Aggressive Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "204", "firstAnchor": { "contextRef": "S000091984_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R205": { "role": "http://www.northwesternmutual.com/26/role/PerformanceManagement", "longName": "2610005 - Disclosure - Active Passive Very Aggressive Portfolio Performance Management", "shortName": "Active Passive Very Aggressive Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "205", "firstAnchor": { "contextRef": "S000091984", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R206": { "role": "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "longName": "2620010 - Disclosure - Active Passive Very Aggressive Portfolio Shareholder Fees", "shortName": "Active Passive Very Aggressive Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "206", "firstAnchor": null, "uniqueAnchor": null }, "R207": { "role": "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "longName": "2620020 - Disclosure - Active Passive Very Aggressive Portfolio Annual Fund Operating Expenses", "shortName": "Active Passive Very Aggressive Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "207", "firstAnchor": { "contextRef": "S000091984", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R208": { "role": "http://www.northwesternmutual.com/26/role/ExpenseExample", "longName": "2620030 - Disclosure - Active Passive Very Aggressive Portfolio Expense Example", "shortName": "Active Passive Very Aggressive Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "208", "firstAnchor": { "contextRef": "S000091984_C000259890", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091984_C000259890", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R209": { "role": "http://www.northwesternmutual.com/27/role/N1aCover", "longName": "2710000 - Disclosure - Active Passive Aggressive Portfolio N-1A Cover", "shortName": "Active Passive Aggressive Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "209", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R210": { "role": "http://www.northwesternmutual.com/27/role/RiskReturn", "longName": "2710001 - Disclosure - Active Passive Aggressive Portfolio Investment Objectives and Goals", "shortName": "Active Passive Aggressive Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "210", "firstAnchor": { "contextRef": "S000091983", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R211": { "role": "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "longName": "2710002 - Disclosure - Active Passive Aggressive Portfolio Fees and Expenses", "shortName": "Active Passive Aggressive Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "211", "firstAnchor": { "contextRef": "S000091983", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R212": { "role": "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "longName": "2710003 - Disclosure - Active Passive Aggressive Portfolio Investment Strategy", "shortName": "Active Passive Aggressive Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "212", "firstAnchor": { "contextRef": "S000091983", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R213": { "role": "http://www.northwesternmutual.com/27/role/InvestmentRisks", "longName": "2710004 - Disclosure - Active Passive Aggressive Portfolio Investment Risks", "shortName": "Active Passive Aggressive Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "213", "firstAnchor": { "contextRef": "S000091983_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R214": { "role": "http://www.northwesternmutual.com/27/role/PerformanceManagement", "longName": "2710005 - Disclosure - Active Passive Aggressive Portfolio Performance Management", "shortName": "Active Passive Aggressive Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "214", "firstAnchor": { "contextRef": "S000091983", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R215": { "role": "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "longName": "2720010 - Disclosure - Active Passive Aggressive Portfolio Shareholder Fees", "shortName": "Active Passive Aggressive Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "215", "firstAnchor": null, "uniqueAnchor": null }, "R216": { "role": "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "longName": "2720020 - Disclosure - Active Passive Aggressive Portfolio Annual Fund Operating Expenses", "shortName": "Active Passive Aggressive Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "216", "firstAnchor": { "contextRef": "S000091983", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R217": { "role": "http://www.northwesternmutual.com/27/role/ExpenseExample", "longName": "2720030 - Disclosure - Active Passive Aggressive Portfolio Expense Example", "shortName": "Active Passive Aggressive Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "217", "firstAnchor": { "contextRef": "S000091983_C000259889", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091983_C000259889", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R218": { "role": "http://www.northwesternmutual.com/28/role/N1aCover", "longName": "2810000 - Disclosure - Active Passive Moderate Portfolio N-1A Cover", "shortName": "Active Passive Moderate Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "218", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R219": { "role": "http://www.northwesternmutual.com/28/role/RiskReturn", "longName": "2810001 - Disclosure - Active Passive Moderate Portfolio Investment Objectives and Goals", "shortName": "Active Passive Moderate Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "219", "firstAnchor": { "contextRef": "S000000044", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R220": { "role": "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "longName": "2810002 - Disclosure - Active Passive Moderate Portfolio Fees and Expenses", "shortName": "Active Passive Moderate Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "220", "firstAnchor": { "contextRef": "S000000044", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R221": { "role": "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "longName": "2810003 - Disclosure - Active Passive Moderate Portfolio Investment Strategy", "shortName": "Active Passive Moderate Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "221", "firstAnchor": { "contextRef": "S000000044", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R222": { "role": "http://www.northwesternmutual.com/28/role/InvestmentRisks", "longName": "2810004 - Disclosure - Active Passive Moderate Portfolio Investment Risks", "shortName": "Active Passive Moderate Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "222", "firstAnchor": { "contextRef": "S000000044_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R223": { "role": "http://www.northwesternmutual.com/28/role/PerformanceManagement", "longName": "2810005 - Disclosure - Active Passive Moderate Portfolio Performance Management", "shortName": "Active Passive Moderate Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "223", "firstAnchor": { "contextRef": "S000000044", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R224": { "role": "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "longName": "2820010 - Disclosure - Active Passive Moderate Portfolio Shareholder Fees", "shortName": "Active Passive Moderate Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "224", "firstAnchor": null, "uniqueAnchor": null }, "R225": { "role": "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "longName": "2820020 - Disclosure - Active Passive Moderate Portfolio Annual Fund Operating Expenses", "shortName": "Active Passive Moderate Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "225", "firstAnchor": { "contextRef": "S000000044", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R226": { "role": "http://www.northwesternmutual.com/28/role/ExpenseExample", "longName": "2820030 - Disclosure - Active Passive Moderate Portfolio Expense Example", "shortName": "Active Passive Moderate Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "226", "firstAnchor": { "contextRef": "S000000044_C000000079", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000044_C000000079", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R227": { "role": "http://www.northwesternmutual.com/28/role/BarChartData", "longName": "2820050 - Disclosure - Active Passive Moderate Portfolio Annual Total Returns", "shortName": "Active Passive Moderate Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "227", "firstAnchor": null, "uniqueAnchor": null }, "R228": { "role": "http://www.northwesternmutual.com/28/role/PerformanceTableData", "longName": "2820060 - Disclosure - Active Passive Moderate Portfolio Average Annual Total Returns", "shortName": "Active Passive Moderate Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "228", "firstAnchor": { "contextRef": "_ActivePassiveModeratePortfolioBlendedCompositeBenchmarkMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_ActivePassiveModeratePortfolioBlendedCompositeBenchmarkMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R229": { "role": "http://www.northwesternmutual.com/29/role/N1aCover", "longName": "2910000 - Disclosure - Active Passive Balanced Portfolio N-1A Cover", "shortName": "Active Passive Balanced Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "229", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R230": { "role": "http://www.northwesternmutual.com/29/role/RiskReturn", "longName": "2910001 - Disclosure - Active Passive Balanced Portfolio Investment Objectives and Goals", "shortName": "Active Passive Balanced Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "230", "firstAnchor": { "contextRef": "S000000045", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R231": { "role": "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "longName": "2910002 - Disclosure - Active Passive Balanced Portfolio Fees and Expenses", "shortName": "Active Passive Balanced Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "231", "firstAnchor": { "contextRef": "S000000045", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R232": { "role": "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "longName": "2910003 - Disclosure - Active Passive Balanced Portfolio Investment Strategy", "shortName": "Active Passive Balanced Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "232", "firstAnchor": { "contextRef": "S000000045", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R233": { "role": "http://www.northwesternmutual.com/29/role/InvestmentRisks", "longName": "2910004 - Disclosure - Active Passive Balanced Portfolio Investment Risks", "shortName": "Active Passive Balanced Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "233", "firstAnchor": { "contextRef": "S000000045_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R234": { "role": "http://www.northwesternmutual.com/29/role/PerformanceManagement", "longName": "2910005 - Disclosure - Active Passive Balanced Portfolio Performance Management", "shortName": "Active Passive Balanced Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "234", "firstAnchor": { "contextRef": "S000000045", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R235": { "role": "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "longName": "2920010 - Disclosure - Active Passive Balanced Portfolio Shareholder Fees", "shortName": "Active Passive Balanced Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "235", "firstAnchor": null, "uniqueAnchor": null }, "R236": { "role": "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "longName": "2920020 - Disclosure - Active Passive Balanced Portfolio Annual Fund Operating Expenses", "shortName": "Active Passive Balanced Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "236", "firstAnchor": { "contextRef": "S000000045", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R237": { "role": "http://www.northwesternmutual.com/29/role/ExpenseExample", "longName": "2920030 - Disclosure - Active Passive Balanced Portfolio Expense Example", "shortName": "Active Passive Balanced Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "237", "firstAnchor": { "contextRef": "S000000045_C000000080", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000045_C000000080", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R238": { "role": "http://www.northwesternmutual.com/29/role/BarChartData", "longName": "2920050 - Disclosure - Active Passive Balanced Portfolio Annual Total Returns", "shortName": "Active Passive Balanced Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "238", "firstAnchor": null, "uniqueAnchor": null }, "R239": { "role": "http://www.northwesternmutual.com/29/role/PerformanceTableData", "longName": "2920060 - Disclosure - Active Passive Balanced Portfolio Average Annual Total Returns", "shortName": "Active Passive Balanced Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "239", "firstAnchor": { "contextRef": "_ActivePassiveBalancedPortfolioBlendedCompositeBenchmarkMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_ActivePassiveBalancedPortfolioBlendedCompositeBenchmarkMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R240": { "role": "http://www.northwesternmutual.com/30/role/N1aCover", "longName": "3010000 - Disclosure - Active Passive Conservative Portfolio N-1A Cover", "shortName": "Active Passive Conservative Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "240", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R241": { "role": "http://www.northwesternmutual.com/30/role/RiskReturn", "longName": "3010001 - Disclosure - Active Passive Conservative Portfolio Investment Objectives and Goals", "shortName": "Active Passive Conservative Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "241", "firstAnchor": { "contextRef": "S000091982", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R242": { "role": "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "longName": "3010002 - Disclosure - Active Passive Conservative Portfolio Fees and Expenses", "shortName": "Active Passive Conservative Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "242", "firstAnchor": { "contextRef": "S000091982", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R243": { "role": "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "longName": "3010003 - Disclosure - Active Passive Conservative Portfolio Investment Strategy", "shortName": "Active Passive Conservative Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "243", "firstAnchor": { "contextRef": "S000091982", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R244": { "role": "http://www.northwesternmutual.com/30/role/InvestmentRisks", "longName": "3010004 - Disclosure - Active Passive Conservative Portfolio Investment Risks", "shortName": "Active Passive Conservative Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "244", "firstAnchor": { "contextRef": "S000091982_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R245": { "role": "http://www.northwesternmutual.com/30/role/PerformanceManagement", "longName": "3010005 - Disclosure - Active Passive Conservative Portfolio Performance Management", "shortName": "Active Passive Conservative Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "245", "firstAnchor": { "contextRef": "S000091982", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R246": { "role": "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "longName": "3020010 - Disclosure - Active Passive Conservative Portfolio Shareholder Fees", "shortName": "Active Passive Conservative Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "246", "firstAnchor": null, "uniqueAnchor": null }, "R247": { "role": "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "longName": "3020020 - Disclosure - Active Passive Conservative Portfolio Annual Fund Operating Expenses", "shortName": "Active Passive Conservative Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "247", "firstAnchor": { "contextRef": "S000091982", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R248": { "role": "http://www.northwesternmutual.com/30/role/ExpenseExample", "longName": "3020030 - Disclosure - Active Passive Conservative Portfolio Expense Example", "shortName": "Active Passive Conservative Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "248", "firstAnchor": { "contextRef": "S000091982_C000259888", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000091982_C000259888", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R249": { "role": "http://www.northwesternmutual.com/3/role/N1aCover", "longName": "310000 - Disclosure - Large Cap Core Stock Portfolio N-1A Cover", "shortName": "Large Cap Core Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "249", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R250": { "role": "http://www.northwesternmutual.com/3/role/RiskReturn", "longName": "310001 - Disclosure - Large Cap Core Stock Portfolio Investment Objectives and Goals", "shortName": "Large Cap Core Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "250", "firstAnchor": { "contextRef": "S000000040", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R251": { "role": "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "longName": "310002 - Disclosure - Large Cap Core Stock Portfolio Fees and Expenses", "shortName": "Large Cap Core Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "251", "firstAnchor": { "contextRef": "S000000040", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R252": { "role": "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "longName": "310003 - Disclosure - Large Cap Core Stock Portfolio Investment Strategy", "shortName": "Large Cap Core Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "252", "firstAnchor": { "contextRef": "S000000040", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R253": { "role": "http://www.northwesternmutual.com/3/role/InvestmentRisks", "longName": "310004 - Disclosure - Large Cap Core Stock Portfolio Investment Risks", "shortName": "Large Cap Core Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "253", "firstAnchor": { "contextRef": "S000000040_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R254": { "role": "http://www.northwesternmutual.com/3/role/PerformanceManagement", "longName": "310005 - Disclosure - Large Cap Core Stock Portfolio Performance Management", "shortName": "Large Cap Core Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "254", "firstAnchor": { "contextRef": "S000000040", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R255": { "role": "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "longName": "320010 - Disclosure - Large Cap Core Stock Portfolio Shareholder Fees", "shortName": "Large Cap Core Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "255", "firstAnchor": null, "uniqueAnchor": null }, "R256": { "role": "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "longName": "320020 - Disclosure - Large Cap Core Stock Portfolio Annual Fund Operating Expenses", "shortName": "Large Cap Core Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "256", "firstAnchor": { "contextRef": "S000000040", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R257": { "role": "http://www.northwesternmutual.com/3/role/ExpenseExample", "longName": "320030 - Disclosure - Large Cap Core Stock Portfolio Expense Example", "shortName": "Large Cap Core Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "257", "firstAnchor": { "contextRef": "S000000040_C000000075", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000040_C000000075", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R258": { "role": "http://www.northwesternmutual.com/3/role/BarChartData", "longName": "320050 - Disclosure - Large Cap Core Stock Portfolio Annual Total Returns", "shortName": "Large Cap Core Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "258", "firstAnchor": null, "uniqueAnchor": null }, "R259": { "role": "http://www.northwesternmutual.com/3/role/PerformanceTableData", "longName": "320060 - Disclosure - Large Cap Core Stock Portfolio Average Annual Total Returns", "shortName": "Large Cap Core Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "259", "firstAnchor": { "contextRef": "_SP500IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000075_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R260": { "role": "http://www.northwesternmutual.com/4/role/N1aCover", "longName": "410000 - Disclosure - Large Cap Blend Portfolio N-1A Cover", "shortName": "Large Cap Blend Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "260", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R261": { "role": "http://www.northwesternmutual.com/4/role/RiskReturn", "longName": "410001 - Disclosure - Large Cap Blend Portfolio Investment Objectives and Goals", "shortName": "Large Cap Blend Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "261", "firstAnchor": { "contextRef": "S000018229", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R262": { "role": "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "longName": "410002 - Disclosure - Large Cap Blend Portfolio Fees and Expenses", "shortName": "Large Cap Blend Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "262", "firstAnchor": { "contextRef": "S000018229", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R263": { "role": "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "longName": "410003 - Disclosure - Large Cap Blend Portfolio Investment Strategy", "shortName": "Large Cap Blend Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "263", "firstAnchor": { "contextRef": "S000018229", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R264": { "role": "http://www.northwesternmutual.com/4/role/InvestmentRisks", "longName": "410004 - Disclosure - Large Cap Blend Portfolio Investment Risks", "shortName": "Large Cap Blend Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "264", "firstAnchor": { "contextRef": "S000018229_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R265": { "role": "http://www.northwesternmutual.com/4/role/PerformanceManagement", "longName": "410005 - Disclosure - Large Cap Blend Portfolio Performance Management", "shortName": "Large Cap Blend Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "265", "firstAnchor": { "contextRef": "S000018229", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R266": { "role": "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "longName": "420010 - Disclosure - Large Cap Blend Portfolio Shareholder Fees", "shortName": "Large Cap Blend Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "266", "firstAnchor": null, "uniqueAnchor": null }, "R267": { "role": "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "longName": "420020 - Disclosure - Large Cap Blend Portfolio Annual Fund Operating Expenses", "shortName": "Large Cap Blend Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "267", "firstAnchor": { "contextRef": "S000018229", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R268": { "role": "http://www.northwesternmutual.com/4/role/ExpenseExample", "longName": "420030 - Disclosure - Large Cap Blend Portfolio Expense Example", "shortName": "Large Cap Blend Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "268", "firstAnchor": { "contextRef": "S000018229_C000050277", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018229_C000050277", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R269": { "role": "http://www.northwesternmutual.com/4/role/BarChartData", "longName": "420050 - Disclosure - Large Cap Blend Portfolio Annual Total Returns", "shortName": "Large Cap Blend Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "269", "firstAnchor": null, "uniqueAnchor": null }, "R270": { "role": "http://www.northwesternmutual.com/4/role/PerformanceTableData", "longName": "420060 - Disclosure - Large Cap Blend Portfolio Average Annual Total Returns", "shortName": "Large Cap Blend Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "270", "firstAnchor": { "contextRef": "_SP500IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000050277_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R271": { "role": "http://www.northwesternmutual.com/5/role/N1aCover", "longName": "510000 - Disclosure - Index 500 Stock Portfolio N-1A Cover", "shortName": "Index 500 Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "271", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R272": { "role": "http://www.northwesternmutual.com/5/role/RiskReturn", "longName": "510001 - Disclosure - Index 500 Stock Portfolio Investment Objectives and Goals", "shortName": "Index 500 Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "272", "firstAnchor": { "contextRef": "S000000043", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R273": { "role": "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "longName": "510002 - Disclosure - Index 500 Stock Portfolio Fees and Expenses", "shortName": "Index 500 Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "273", "firstAnchor": { "contextRef": "S000000043", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R274": { "role": "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "longName": "510003 - Disclosure - Index 500 Stock Portfolio Investment Strategy", "shortName": "Index 500 Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "274", "firstAnchor": { "contextRef": "S000000043", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R275": { "role": "http://www.northwesternmutual.com/5/role/InvestmentRisks", "longName": "510004 - Disclosure - Index 500 Stock Portfolio Investment Risks", "shortName": "Index 500 Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "275", "firstAnchor": { "contextRef": "S000000043_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043_DerivativesRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R276": { "role": "http://www.northwesternmutual.com/5/role/PerformanceManagement", "longName": "510005 - Disclosure - Index 500 Stock Portfolio Performance Management", "shortName": "Index 500 Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "276", "firstAnchor": { "contextRef": "S000000043", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R277": { "role": "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "longName": "520010 - Disclosure - Index 500 Stock Portfolio Shareholder Fees", "shortName": "Index 500 Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "277", "firstAnchor": null, "uniqueAnchor": null }, "R278": { "role": "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "longName": "520020 - Disclosure - Index 500 Stock Portfolio Annual Fund Operating Expenses", "shortName": "Index 500 Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "278", "firstAnchor": { "contextRef": "S000000043", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R279": { "role": "http://www.northwesternmutual.com/5/role/ExpenseExample", "longName": "520030 - Disclosure - Index 500 Stock Portfolio Expense Example", "shortName": "Index 500 Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "279", "firstAnchor": { "contextRef": "S000000043_C000000078", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000043_C000000078", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R280": { "role": "http://www.northwesternmutual.com/5/role/BarChartData", "longName": "520050 - Disclosure - Index 500 Stock Portfolio Annual Total Returns", "shortName": "Index 500 Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "280", "firstAnchor": null, "uniqueAnchor": null }, "R281": { "role": "http://www.northwesternmutual.com/5/role/PerformanceTableData", "longName": "520060 - Disclosure - Index 500 Stock Portfolio Average Annual Total Returns", "shortName": "Index 500 Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "281", "firstAnchor": { "contextRef": "_SP500IndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000078_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R282": { "role": "http://www.northwesternmutual.com/6/role/N1aCover", "longName": "610000 - Disclosure - Large Company Value Portfolio N-1A Cover", "shortName": "Large Company Value Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "282", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R283": { "role": "http://www.northwesternmutual.com/6/role/RiskReturn", "longName": "610001 - Disclosure - Large Company Value Portfolio Investment Objectives and Goals", "shortName": "Large Company Value Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "283", "firstAnchor": { "contextRef": "S000018227", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R284": { "role": "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "longName": "610002 - Disclosure - Large Company Value Portfolio Fees and Expenses", "shortName": "Large Company Value Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "284", "firstAnchor": { "contextRef": "S000018227", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R285": { "role": "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "longName": "610003 - Disclosure - Large Company Value Portfolio Investment Strategy", "shortName": "Large Company Value Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "285", "firstAnchor": { "contextRef": "S000018227", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R286": { "role": "http://www.northwesternmutual.com/6/role/InvestmentRisks", "longName": "610004 - Disclosure - Large Company Value Portfolio Investment Risks", "shortName": "Large Company Value Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "286", "firstAnchor": { "contextRef": "S000018227_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R287": { "role": "http://www.northwesternmutual.com/6/role/PerformanceManagement", "longName": "610005 - Disclosure - Large Company Value Portfolio Performance Management", "shortName": "Large Company Value Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "287", "firstAnchor": { "contextRef": "S000018227", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R288": { "role": "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "longName": "620010 - Disclosure - Large Company Value Portfolio Shareholder Fees", "shortName": "Large Company Value Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "288", "firstAnchor": null, "uniqueAnchor": null }, "R289": { "role": "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "longName": "620020 - Disclosure - Large Company Value Portfolio Annual Fund Operating Expenses", "shortName": "Large Company Value Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "289", "firstAnchor": { "contextRef": "S000018227", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R290": { "role": "http://www.northwesternmutual.com/6/role/ExpenseExample", "longName": "620030 - Disclosure - Large Company Value Portfolio Expense Example", "shortName": "Large Company Value Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "290", "firstAnchor": { "contextRef": "S000018227_C000050275", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000018227_C000050275", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R291": { "role": "http://www.northwesternmutual.com/6/role/BarChartData", "longName": "620050 - Disclosure - Large Company Value Portfolio Annual Total Returns", "shortName": "Large Company Value Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "291", "firstAnchor": null, "uniqueAnchor": null }, "R292": { "role": "http://www.northwesternmutual.com/6/role/PerformanceTableData", "longName": "620060 - Disclosure - Large Company Value Portfolio Average Annual Total Returns", "shortName": "Large Company Value Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "292", "firstAnchor": { "contextRef": "_Russell1000ValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000050275_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R293": { "role": "http://www.northwesternmutual.com/7/role/N1aCover", "longName": "710000 - Disclosure - Domestic Equity Portfolio N-1A Cover", "shortName": "Domestic Equity Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "293", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R294": { "role": "http://www.northwesternmutual.com/7/role/RiskReturn", "longName": "710001 - Disclosure - Domestic Equity Portfolio Investment Objectives and Goals", "shortName": "Domestic Equity Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "294", "firstAnchor": { "contextRef": "S000000041", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R295": { "role": "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "longName": "710002 - Disclosure - Domestic Equity Portfolio Fees and Expenses", "shortName": "Domestic Equity Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "295", "firstAnchor": { "contextRef": "S000000041", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R296": { "role": "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "longName": "710003 - Disclosure - Domestic Equity Portfolio Investment Strategy", "shortName": "Domestic Equity Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "296", "firstAnchor": { "contextRef": "S000000041", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R297": { "role": "http://www.northwesternmutual.com/7/role/InvestmentRisks", "longName": "710004 - Disclosure - Domestic Equity Portfolio Investment Risks", "shortName": "Domestic Equity Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "297", "firstAnchor": { "contextRef": "S000000041_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R298": { "role": "http://www.northwesternmutual.com/7/role/PerformanceManagement", "longName": "710005 - Disclosure - Domestic Equity Portfolio Performance Management", "shortName": "Domestic Equity Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "298", "firstAnchor": { "contextRef": "S000000041", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R299": { "role": "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "longName": "720010 - Disclosure - Domestic Equity Portfolio Shareholder Fees", "shortName": "Domestic Equity Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "299", "firstAnchor": null, "uniqueAnchor": null }, "R300": { "role": "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "longName": "720020 - Disclosure - Domestic Equity Portfolio Annual Fund Operating Expenses", "shortName": "Domestic Equity Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "300", "firstAnchor": { "contextRef": "S000000041", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R301": { "role": "http://www.northwesternmutual.com/7/role/ExpenseExample", "longName": "720030 - Disclosure - Domestic Equity Portfolio Expense Example", "shortName": "Domestic Equity Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "301", "firstAnchor": { "contextRef": "S000000041_C000000076", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000041_C000000076", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R302": { "role": "http://www.northwesternmutual.com/7/role/BarChartData", "longName": "720050 - Disclosure - Domestic Equity Portfolio Annual Total Returns", "shortName": "Domestic Equity Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "302", "firstAnchor": null, "uniqueAnchor": null }, "R303": { "role": "http://www.northwesternmutual.com/7/role/PerformanceTableData", "longName": "720060 - Disclosure - Domestic Equity Portfolio Average Annual Total Returns", "shortName": "Domestic Equity Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "303", "firstAnchor": { "contextRef": "_Russell1000ValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000076_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R304": { "role": "http://www.northwesternmutual.com/8/role/N1aCover", "longName": "810000 - Disclosure - Equity Income Portfolio N-1A Cover", "shortName": "Equity Income Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "304", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R305": { "role": "http://www.northwesternmutual.com/8/role/RiskReturn", "longName": "810001 - Disclosure - Equity Income Portfolio Investment Objectives and Goals", "shortName": "Equity Income Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "305", "firstAnchor": { "contextRef": "S000000042", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R306": { "role": "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "longName": "810002 - Disclosure - Equity Income Portfolio Fees and Expenses", "shortName": "Equity Income Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "306", "firstAnchor": { "contextRef": "S000000042", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R307": { "role": "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "longName": "810003 - Disclosure - Equity Income Portfolio Investment Strategy", "shortName": "Equity Income Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "307", "firstAnchor": { "contextRef": "S000000042", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R308": { "role": "http://www.northwesternmutual.com/8/role/InvestmentRisks", "longName": "810004 - Disclosure - Equity Income Portfolio Investment Risks", "shortName": "Equity Income Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "308", "firstAnchor": { "contextRef": "S000000042_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R309": { "role": "http://www.northwesternmutual.com/8/role/PerformanceManagement", "longName": "810005 - Disclosure - Equity Income Portfolio Performance Management", "shortName": "Equity Income Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "309", "firstAnchor": { "contextRef": "S000000042", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R310": { "role": "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "longName": "820010 - Disclosure - Equity Income Portfolio Shareholder Fees", "shortName": "Equity Income Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "310", "firstAnchor": null, "uniqueAnchor": null }, "R311": { "role": "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "longName": "820020 - Disclosure - Equity Income Portfolio Annual Fund Operating Expenses", "shortName": "Equity Income Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "311", "firstAnchor": { "contextRef": "S000000042", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R312": { "role": "http://www.northwesternmutual.com/8/role/ExpenseExample", "longName": "820030 - Disclosure - Equity Income Portfolio Expense Example", "shortName": "Equity Income Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "312", "firstAnchor": { "contextRef": "S000000042_C000000077", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000042_C000000077", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R313": { "role": "http://www.northwesternmutual.com/8/role/BarChartData", "longName": "820050 - Disclosure - Equity Income Portfolio Annual Total Returns", "shortName": "Equity Income Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "313", "firstAnchor": null, "uniqueAnchor": null }, "R314": { "role": "http://www.northwesternmutual.com/8/role/PerformanceTableData", "longName": "820060 - Disclosure - Equity Income Portfolio Average Annual Total Returns", "shortName": "Equity Income Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "314", "firstAnchor": { "contextRef": "_Russell1000ValueIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": { "contextRef": "C000000077_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "unique": true } }, "R315": { "role": "http://www.northwesternmutual.com/9/role/N1aCover", "longName": "910000 - Disclosure - Mid Cap Growth Stock Portfolio N-1A Cover", "shortName": "Mid Cap Growth Stock Portfolio N-1A Cover", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "315", "firstAnchor": { "contextRef": "D_31Dec2025_31Dec2025", "name": "dei:EntityRegistrantName", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "span", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true }, "uniqueAnchor": null }, "R316": { "role": "http://www.northwesternmutual.com/9/role/RiskReturn", "longName": "910001 - Disclosure - Mid Cap Growth Stock Portfolio Investment Objectives and Goals", "shortName": "Mid Cap Growth Stock Portfolio Investment Objectives and Goals", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "316", "firstAnchor": { "contextRef": "S000000050", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050", "name": "oef:ObjectiveHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R317": { "role": "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "longName": "910002 - Disclosure - Mid Cap Growth Stock Portfolio Fees and Expenses", "shortName": "Mid Cap Growth Stock Portfolio Fees and Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "317", "firstAnchor": { "contextRef": "S000000050", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050", "name": "oef:ExpenseHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R318": { "role": "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "longName": "910003 - Disclosure - Mid Cap Growth Stock Portfolio Investment Strategy", "shortName": "Mid Cap Growth Stock Portfolio Investment Strategy", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "318", "firstAnchor": { "contextRef": "S000000050", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050", "name": "oef:StrategyHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R319": { "role": "http://www.northwesternmutual.com/9/role/InvestmentRisks", "longName": "910004 - Disclosure - Mid Cap Growth Stock Portfolio Investment Risks", "shortName": "Mid Cap Growth Stock Portfolio Investment Risks", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "319", "firstAnchor": { "contextRef": "S000000050_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050_ActiveManagementRiskMember", "name": "oef:RiskTextBlock", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R320": { "role": "http://www.northwesternmutual.com/9/role/PerformanceManagement", "longName": "910005 - Disclosure - Mid Cap Growth Stock Portfolio Performance Management", "shortName": "Mid Cap Growth Stock Portfolio Performance Management", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "320", "firstAnchor": { "contextRef": "S000000050", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050", "name": "oef:BarChartAndPerformanceTableHeading", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R321": { "role": "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "longName": "920010 - Disclosure - Mid Cap Growth Stock Portfolio Shareholder Fees", "shortName": "Mid Cap Growth Stock Portfolio Shareholder Fees", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "321", "firstAnchor": null, "uniqueAnchor": null }, "R322": { "role": "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "longName": "920020 - Disclosure - Mid Cap Growth Stock Portfolio Annual Fund Operating Expenses", "shortName": "Mid Cap Growth Stock Portfolio Annual Fund Operating Expenses", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "322", "firstAnchor": { "contextRef": "S000000050", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050", "name": "oef:FeeWaiverOrReimbursementOverAssetsDateOfTermination", "unitRef": null, "xsiNil": "false", "lang": "en-US", "decimals": null, "ancestors": [ "link:footnote", "div", "div", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R323": { "role": "http://www.northwesternmutual.com/9/role/ExpenseExample", "longName": "920030 - Disclosure - Mid Cap Growth Stock Portfolio Expense Example", "shortName": "Mid Cap Growth Stock Portfolio Expense Example", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "323", "firstAnchor": { "contextRef": "S000000050_C000000085", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "S000000050_C000000085", "name": "oef:ExpenseExampleYear01", "unitRef": "USD", "xsiNil": "false", "lang": null, "decimals": "INF", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } }, "R324": { "role": "http://www.northwesternmutual.com/9/role/BarChartData", "longName": "920050 - Disclosure - Mid Cap Growth Stock Portfolio Annual Total Returns", "shortName": "Mid Cap Growth Stock Portfolio Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "324", "firstAnchor": null, "uniqueAnchor": null }, "R325": { "role": "http://www.northwesternmutual.com/9/role/PerformanceTableData", "longName": "920060 - Disclosure - Mid Cap Growth Stock Portfolio Average Annual Total Returns", "shortName": "Mid Cap Growth Stock Portfolio Average Annual Total Returns", "isDefault": "false", "groupType": "disclosure", "subGroupType": "", "menuCat": "Risk/Return", "order": "325", "firstAnchor": { "contextRef": "_RussellMidCapGrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true }, "uniqueAnchor": { "contextRef": "_RussellMidCapGrowthIndexMember_01Jan2025_31Dec2025", "name": "oef:AvgAnnlRtrPct", "unitRef": "pure", "xsiNil": "false", "lang": null, "decimals": "4", "ancestors": [ "span", "div", "div", "td", "tr", "table", "div", "div", "div", "div", "div", "div", "body", "html" ], "reportCount": 1, "baseRef": "d54223d485bpos.htm", "first": true, "unique": true } } }, "tag": { "nmsf_ADRRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ADRRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "ADR Risk [Member]" } } }, "auth_ref": [] }, "oef_AcquiredFundFeesAndExpensesBasedOnEstimates": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AcquiredFundFeesAndExpensesBasedOnEstimates", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Acquired Fund Fees and Expenses, Based on Estimates [Text]" } } }, "auth_ref": [ "r27" ] }, "oef_AcquiredFundFeesAndExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AcquiredFundFeesAndExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_ExpensesOverAssets", "weight": 1.0, "order": 5.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Acquired Fund Fees and Expenses" } } }, "auth_ref": [ "r26" ] }, "nmsf_ActiveManagementRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ActiveManagementRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Active Management Risk [Member]" } } }, "auth_ref": [] }, "nmsf_ActivePassiveBalancedPortfolioBlendedCompositeBenchmarkMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ActivePassiveBalancedPortfolioBlendedCompositeBenchmarkMember", "presentation": [ "http://www.northwesternmutual.com/29/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Active/Passive Balanced Portfolio Blended Composite Benchmark: S&P 500® Index (17%), S&P MidCap 400® Index (5%), S&P SmallCap 600® Index (3%), MSCI EAFE® Index (10%), MSCI® Emerging Markets Index (5%), Dow Jones U.S. Select REIT Index (4%), Bloomberg® Commodity IndexSM (4%), Bloomberg® Barclays U.S. Aggregate Bond Index (50%), and ICE of BofA® US 3-Month Treasury Bill Index (2%)[Member]" } } }, "auth_ref": [] }, "nmsf_ActivePassiveModeratePortfolioBlendedCompositeBenchmarkMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ActivePassiveModeratePortfolioBlendedCompositeBenchmarkMember", "presentation": [ "http://www.northwesternmutual.com/28/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Active/Passive Moderate Portfolio Blended Composite Benchmark: S&P 500® Index (28%), S&P 400® MidCap Index (7%), S&P SmallCap 600® Index (3%), MSCI EAFE® Index (15%), MSCI® Emerging Markets Index (6%), Dow Jones U.S. Select REIT Index (4%), Bloomberg® Commodity IndexSM (5%), Bloomberg® Barclays U.S. Aggregate Bond Index (30%), and ICE of BofA® US 3-Month Treasury Bill Index (2%)[Member]" } } }, "auth_ref": [] }, "nmsf_AffiliatedPortfolioRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "AffiliatedPortfolioRiskMember", "presentation": [ "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Affiliated Portfolio Risk [Member]" } } }, "auth_ref": [] }, "oef_AfterTaxesOnDistributionsAndSalesMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AfterTaxesOnDistributionsAndSalesMember", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "After Taxes on Distributions and Sales" } } }, "auth_ref": [ "r47" ] }, "oef_AfterTaxesOnDistributionsMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AfterTaxesOnDistributionsMember", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "After Taxes on Distributions" } } }, "auth_ref": [ "r47" ] }, "oef_AllRisksMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AllRisksMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "All Risks [Member]" } } }, "auth_ref": [ "r36" ] }, "dei_AmendmentDescription": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "AmendmentDescription", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Amendment Description", "documentation": "Description of changes contained within amended document." } } }, "auth_ref": [] }, "dei_AmendmentFlag": { "xbrltype": "booleanItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "AmendmentFlag", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Amendment Flag", "documentation": "Boolean flag that is true when the XBRL content amends previously-filed or accepted submission." } } }, "auth_ref": [] }, "oef_AnnlRtrPct": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AnnlRtrPct", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://xbrl.sec.gov/rr/role/BarChartData" ], "lang": { "en-us": { "role": { "label": "Annual Return [Percent]" } } }, "auth_ref": [ "r43" ] }, "oef_AnnualFundOperatingExpensesTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AnnualFundOperatingExpensesTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Annual Fund Operating Expenses [Table]" } } }, "auth_ref": [ "r33" ] }, "oef_AnnualReturnCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AnnualReturnCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://xbrl.sec.gov/rr/role/BarChartData" ], "lang": { "en-us": { "role": { "label": "Annual Return Caption [Text]" } } }, "auth_ref": [ "r45" ] }, "oef_AnnualReturnColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AnnualReturnColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://xbrl.sec.gov/rr/role/BarChartData" ], "lang": { "en-us": { "role": { "label": "Annual Return, Column [Optional Text]" } } }, "auth_ref": [ "r44" ] }, "oef_AnnualReturnInceptionDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AnnualReturnInceptionDate", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://xbrl.sec.gov/rr/role/BarChartData" ], "lang": { "en-us": { "role": { "label": "Annual Return, Inception Date" } } }, "auth_ref": [ "r43" ] }, "nmsf_AssetAllocationRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "AssetAllocationRiskMember", "presentation": [ "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Asset Allocation Risk [Member]" } } }, "auth_ref": [] }, "oef_AverageAnnualReturnAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AverageAnnualReturnAbstract", "lang": { "en-us": { "role": { "label": "Average Annual Return:" } } }, "auth_ref": [ "r47" ] }, "oef_AverageAnnualReturnCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AverageAnnualReturnCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Average Annual Return, Caption [Optional Text]" } } }, "auth_ref": [ "r47" ] }, "oef_AverageAnnualReturnColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AverageAnnualReturnColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Average Annual Return, Column Name [Optional Text]" } } }, "auth_ref": [ "r47" ] }, "oef_AverageAnnualReturnLabel": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AverageAnnualReturnLabel", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Average Annual Return, Label [Optional Text]" } } }, "auth_ref": [ "r47" ] }, "oef_AvgAnnlRtrPct": { "xbrltype": "percentItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "AvgAnnlRtrPct", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Average Annual Return, Percent" } } }, "auth_ref": [ "r8" ] }, "oef_BarChartAndPerformanceTableHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartAndPerformanceTableHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart and Performance Table [Heading]" } } }, "auth_ref": [ "r41" ] }, "oef_BarChartClosingTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartClosingTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart Closing [Text Block]" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartDoesNotReflectSalesLoads": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartDoesNotReflectSalesLoads", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart Does Not Reflect Sales Loads [Text]" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartFootnotesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartFootnotesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart Footnotes [Text Block]" } } }, "auth_ref": [ "r48" ] }, "oef_BarChartHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart [Heading]" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartHighestQuarterlyReturn": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartHighestQuarterlyReturn", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Highest Quarterly Return" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartHighestQuarterlyReturnDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartHighestQuarterlyReturnDate", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Highest Quarterly Return, Date" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartLowestQuarterlyReturn": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartLowestQuarterlyReturn", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Lowest Quarterly Return" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartLowestQuarterlyReturnDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartLowestQuarterlyReturnDate", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Lowest Quarterly Return, Date" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart Narrative [Text Block]" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartReasonSelectedClassDifferentFromImmediatelyPrecedingPeriod": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartReasonSelectedClassDifferentFromImmediatelyPrecedingPeriod", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text]" } } }, "auth_ref": [ "r46" ] }, "oef_BarChartReturnsForClassNotOfferedInProspectus": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartReturnsForClassNotOfferedInProspectus", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart, Returns for Class Not Offered in Prospectus [Text]" } } }, "auth_ref": [ "r45" ] }, "oef_BarChartTableAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartTableAbstract", "lang": { "en-us": { "role": { "label": "Bar Chart Table:" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart [Table]" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartYearToDateReturn": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartYearToDateReturn", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart, Year to Date Return" } } }, "auth_ref": [ "r43" ] }, "oef_BarChartYearToDateReturnDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "BarChartYearToDateReturnDate", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Bar Chart, Year to Date Return, Date" } } }, "auth_ref": [ "r43" ] }, "nmsf_Bloomberg13YrUSGovtCreditBondIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "Bloomberg13YrUSGovtCreditBondIndexMember", "presentation": [ "http://www.northwesternmutual.com/20/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® 1-3 Year U.S. Government/Credit Bond Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_BloombergGlobalAggregateIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "BloombergGlobalAggregateIndexMember", "presentation": [ "http://www.northwesternmutual.com/25/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® Global Aggregate Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_BloombergLongTermTreasuryIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "BloombergLongTermTreasuryIndexMember", "presentation": [ "http://www.northwesternmutual.com/22/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® Long-Term Treasury Index[Member]" } } }, "auth_ref": [] }, "nmsf_BloombergUSAggregateBondIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "BloombergUSAggregateBondIndexMember", "presentation": [ "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® U.S. Aggregate Bond Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_BloombergUSCorporateHighYield2PercentIssuerCappedIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "BloombergUSCorporateHighYield2PercentIssuerCappedIndexMember", "presentation": [ "http://www.northwesternmutual.com/24/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® U.S. Corporate High Yield 2% Issuer Capped Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_BloombergUSTreasuryInflationProtectedSecuritiesTIPSIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "BloombergUSTreasuryInflationProtectedSecuritiesTIPSIndexMember", "presentation": [ "http://www.northwesternmutual.com/23/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Bloomberg® U.S. Treasury Inflation Protected Securities (TIPS) Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_C000000074Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000074Member", "presentation": [ "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Small Cap Growth Stock Portfolio", "label": "C000000074 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000075Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000075Member", "presentation": [ "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Cap Core Stock Portfolio", "label": "C000000075 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000076Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000076Member", "presentation": [ "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Domestic Equity Portfolio", "label": "C000000076 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000077Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000077Member", "presentation": [ "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Equity Income Portfolio", "label": "C000000077 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000078Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000078Member", "presentation": [ "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 500 Stock Portfolio", "label": "C000000078 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000079Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000079Member", "presentation": [ "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Asset Allocation Portolio", "label": "C000000079 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000080Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000080Member", "presentation": [ "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Balanced Portfolio", "label": "C000000080 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000081Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000081Member", "presentation": [ "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "High Yield Bond Portfolio", "label": "C000000081 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000082Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000082Member", "presentation": [ "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Select Bond Portfolio", "label": "C000000082 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000083Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000083Member", "presentation": [ "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Government Money Market Portfolio", "label": "C000000083 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000084Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000084Member", "presentation": [ "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Small Cap Value Portfolio", "label": "C000000084 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000085Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000085Member", "presentation": [ "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Mid Cap Growth Stock Portfolio", "label": "C000000085 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000086Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000086Member", "presentation": [ "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "International Growth Portfolio", "label": "C000000086 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000087Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000087Member", "presentation": [ "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "International Equity Portfolio", "label": "C000000087 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000088Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000088Member", "presentation": [ "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Mid Cap Value Portfolio", "label": "C000000088 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000089Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000089Member", "presentation": [ "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 400 Stock Portfolio", "label": "C000000089 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000090Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000090Member", "presentation": [ "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Focused Appreciation Portfolio", "label": "C000000090 [Member]" } } }, "auth_ref": [] }, "nmsf_C000000091Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000000091Member", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Growth Stock Portfolio", "label": "C000000091 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050275Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050275Member", "presentation": [ "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Company Value Portfolio", "label": "C000050275 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050276Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050276Member", "presentation": [ "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Inflation Protectiion Portfolio", "label": "C000050276 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050277Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050277Member", "presentation": [ "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Cap Blend Portfolio", "label": "C000050277 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050278Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050278Member", "presentation": [ "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Research International Core Portfolio", "label": "C000050278 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050279Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050279Member", "presentation": [ "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 600 Stock Portfolio", "label": "C000050279 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050280Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050280Member", "presentation": [ "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Emerging Markets Equity Portfolio", "label": "C000050280 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050281Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050281Member", "presentation": [ "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Short-Term Bond Portfolio", "label": "C000050281 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050282Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050282Member", "presentation": [ "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Long-Term US Government Bond Portfolio", "label": "C000050282 [Member]" } } }, "auth_ref": [] }, "nmsf_C000050283Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000050283Member", "presentation": [ "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Multi-Sector Bond Portfolio", "label": "C000050283 [Member]" } } }, "auth_ref": [] }, "nmsf_C000259888Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000259888Member", "presentation": [ "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Conservative Portfolio", "label": "C000259888 [Member]" } } }, "auth_ref": [] }, "nmsf_C000259889Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000259889Member", "presentation": [ "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Aggressive Portfolio", "label": "C000259889 [Member]" } } }, "auth_ref": [] }, "nmsf_C000259890Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "C000259890Member", "presentation": [ "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive All Equity Portfolio", "label": "C000259890 [Member]" } } }, "auth_ref": [] }, "nmsf_ChinaInvestingRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ChinaInvestingRiskMember", "presentation": [ "http://www.northwesternmutual.com/18/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "China Investing Risk [Member]" } } }, "auth_ref": [] }, "oef_ClassAxis": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ClassAxis", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Class [Axis]" } } }, "auth_ref": [ "r3" ] }, "nmsf_CommoditiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "CommoditiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Commodities Risk [Member]" } } }, "auth_ref": [] }, "oef_Component1OtherExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "Component1OtherExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_OtherExpensesOverAssets", "weight": 1.0, "order": 1.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Component1 Other Expenses" } } }, "auth_ref": [ "r21" ] }, "oef_Component2OtherExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "Component2OtherExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_OtherExpensesOverAssets", "weight": 1.0, "order": 2.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Component2 Other Expenses" } } }, "auth_ref": [ "r21" ] }, "oef_Component3OtherExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "Component3OtherExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_OtherExpensesOverAssets", "weight": 1.0, "order": 3.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Component3 Other Expenses" } } }, "auth_ref": [ "r21" ] }, "nmsf_ContingentConvertibleSecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ContingentConvertibleSecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Contingent Convertible Securities Risk [Member]" } } }, "auth_ref": [] }, "nmsf_ConvertibleSecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ConvertibleSecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Convertible Securities Risk [Member]" } } }, "auth_ref": [] }, "nmsf_CounterpartyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "CounterpartyRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Counterparty Risk [Member]" } } }, "auth_ref": [] }, "us-gaap_CreditRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://fasb.org/us-gaap/2024", "localname": "CreditRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Credit Risk [Member]" } } }, "auth_ref": [] }, "nmsf_DebtObligationsofForeignGovernmentsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "DebtObligationsofForeignGovernmentsRiskMember", "presentation": [ "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Debt Obligations of Foreign Governments Risk [Member]" } } }, "auth_ref": [] }, "nmsf_DerivativesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "DerivativesRiskMember", "presentation": [ "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Derivatives Risk [Member]" } } }, "auth_ref": [] }, "oef_DistributionAndService12b1FeesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "DistributionAndService12b1FeesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_ExpensesOverAssets", "weight": 1.0, "order": 2.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Distribution and Service (12b-1) Fees" } } }, "auth_ref": [ "r18" ] }, "oef_DistributionOrSimilarNon12b1FeesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "DistributionOrSimilarNon12b1FeesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_ExpensesOverAssets", "weight": 1.0, "order": 3.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Distribution or Similar (Non 12b-1) Fees" } } }, "auth_ref": [ "r18" ] }, "nmsf_DividendPayingStockRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "DividendPayingStockRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Dividend-Paying Stock Risk [Member]" } } }, "auth_ref": [] }, "dei_DocumentDomain": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "DocumentDomain", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/N1aCover", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/N1aCover", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Prospectus", "documentation": "Type of the document as assigned by the filer, corresponding to SEC document naming convention standards." } } }, "auth_ref": [] }, "dei_DocumentInformationDocumentAxis": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "DocumentInformationDocumentAxis", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/N1aCover", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/N1aCover", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Document [Axis]", "documentation": "The axis of a table defines the relationship between the domain members or categories in the table and the line items or concepts that complete the table." } } }, "auth_ref": [] }, "dei_DocumentPeriodEndDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "DocumentPeriodEndDate", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Document Period End Date", "documentation": "For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD." } } }, "auth_ref": [] }, "dei_DocumentType": { "xbrltype": "submissionTypeItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "DocumentType", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Document Type", "documentation": "The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'." } } }, "auth_ref": [] }, "nmsf_ESGRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ESGRiskMember", "presentation": [ "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "ESG Risk [Member]" } } }, "auth_ref": [] }, "nmsf_EmergingMarketsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "EmergingMarketsRiskMember", "presentation": [ "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Emerging Markets Risk [Member]" } } }, "auth_ref": [] }, "dei_EntityCentralIndexKey": { "xbrltype": "centralIndexKeyItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "EntityCentralIndexKey", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Entity Central Index Key", "documentation": "A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK." } } }, "auth_ref": [ "r0" ] }, "dei_EntityDomain": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "EntityDomain", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Series", "documentation": "All the names of the entities being reported upon in a document. Any legal structure used to conduct activities or to hold assets. Some examples of such structures are corporations, partnerships, limited liability companies, grantor trusts, and other trusts. This item does not include business and geographical segments which are included in the geographical or business segments domains." } } }, "auth_ref": [] }, "dei_EntityInvCompanyType": { "xbrltype": "invCompanyType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "EntityInvCompanyType", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Entity Investment Company Type", "documentation": "One of: N-1A (Mutual Fund), N-1 (Open-End Separate Account with No Variable Annuities), N-2 (Closed-End Investment Company), N-3 (Separate Account Registered as Open-End Management Investment Company), N-4 (Variable Annuity UIT Separate Account), N-5 (Small Business Investment Company), N-6 (Variable Life UIT Separate Account), S-1 or S-3 (Face Amount Certificate Company), S-6 (UIT, Non-Insurance Product)." } } }, "auth_ref": [ "r58" ] }, "dei_EntityRegistrantName": { "xbrltype": "normalizedStringItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "EntityRegistrantName", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Registrant Name", "documentation": "The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC." } } }, "auth_ref": [ "r0" ] }, "nmsf_EquitySecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "EquitySecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Equity Securities Risk [Member]" } } }, "auth_ref": [] }, "oef_ExchangeFee": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExchangeFee", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Exchange Fee" } } }, "auth_ref": [ "r12" ] }, "oef_ExchangeFeeOverRedemption": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExchangeFeeOverRedemption", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Exchange Fee (as a percentage of Amount Redeemed)" } } }, "auth_ref": [ "r12" ] }, "nmsf_ExchangeTradedFundsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ExchangeTradedFundsRiskMember", "presentation": [ "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Exchange Traded Funds Risk [Member]" } } }, "auth_ref": [] }, "oef_ExpenseBreakpointDiscounts": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseBreakpointDiscounts", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Breakpoint Discounts [Text]" } } }, "auth_ref": [ "r24" ] }, "oef_ExpenseBreakpointMinimumInvestmentRequiredAmount": { "xbrltype": "monetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseBreakpointMinimumInvestmentRequiredAmount", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Breakpoint, Minimum Investment Required [Amount]" } } }, "auth_ref": [ "r11" ] }, "oef_ExpenseExampleAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleAbstract", "lang": { "en-us": { "role": { "label": "Expense Example:" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleByYearCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleByYearCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example by, Year, Caption [Text]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleByYearColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleByYearColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExample" ], "lang": { "en-us": { "role": { "label": "Expense Example, By Year, Column [Optional Text]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleByYearHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleByYearHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example by Year [Heading]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleClosingTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleClosingTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example Closing [Text Block]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleFootnotesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleFootnotesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example Footnotes [Text Block]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example [Heading]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example Narrative [Text Block]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleNoRedemptionAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionAbstract", "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption:" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionByYearCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionByYearCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, By Year, Caption [Text]" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionByYearColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionByYearColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, By Year, Column [Optional Text]" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption Narrative [Text Block]" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption [Table]" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionYear01": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionYear01", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, 1 Year" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionYear03": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionYear03", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, 3 Years" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionYear05": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionYear05", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, 5 Years" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleNoRedemptionYear10": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleNoRedemptionYear10", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption" ], "lang": { "en-us": { "role": { "label": "Expense Example, No Redemption, 10 Years" } } }, "auth_ref": [ "r30" ] }, "oef_ExpenseExampleWithRedemptionTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleWithRedemptionTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Example, With Redemption [Table]" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleYear01": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleYear01", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExample" ], "lang": { "en-us": { "role": { "label": "Expense Example, with Redemption, 1 Year" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleYear03": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleYear03", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExample" ], "lang": { "en-us": { "role": { "label": "Expense Example, with Redemption, 3 Years" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleYear05": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleYear05", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExample" ], "lang": { "en-us": { "role": { "label": "Expense Example, with Redemption, 5 Years" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseExampleYear10": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseExampleYear10", "presentation": [ "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExample" ], "lang": { "en-us": { "role": { "label": "Expense Example, with Redemption, 10 Years" } } }, "auth_ref": [ "r29" ] }, "oef_ExpenseFootnotesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseFootnotesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Footnotes [Text Block]" } } }, "auth_ref": [ "r16" ] }, "oef_ExpenseHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Heading [Optional Text]" } } }, "auth_ref": [ "r10" ] }, "oef_ExpenseNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpenseNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expense Narrative [Text Block]" } } }, "auth_ref": [ "r11" ] }, "oef_ExpensesDeferredChargesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesDeferredChargesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Deferred Charges [Text Block]" } } }, "auth_ref": [ "r13" ] }, "oef_ExpensesExplanationOfNonrecurringAccountFee": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesExplanationOfNonrecurringAccountFee", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Explanation of Nonrecurring Account Fee [Text]" } } }, "auth_ref": [ "r15" ] }, "oef_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesNotCorrelatedToRatioDueToAcquiredFundFees", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]" } } }, "auth_ref": [ "r28" ] }, "oef_ExpensesOtherExpensesHadExtraordinaryExpensesBeenIncluded": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesOtherExpensesHadExtraordinaryExpensesBeenIncluded", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Other Expenses Had Extraordinary Expenses Been Included [Text]" } } }, "auth_ref": [ "r20" ] }, "oef_ExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_NetExpensesOverAssets", "weight": 1.0, "order": 1.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Expenses (as a percentage of Assets)", "totalLabel": "Total Expenses" } } }, "auth_ref": [ "r22" ] }, "oef_ExpensesRangeOfExchangeFeesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesRangeOfExchangeFeesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Range of Exchange Fees [Text Block]" } } }, "auth_ref": [ "r14" ] }, "oef_ExpensesRestatedToReflectCurrent": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ExpensesRestatedToReflectCurrent", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Expenses Restated to Reflect Current [Text]" } } }, "auth_ref": [ "r23" ] }, "oef_FeeWaiverOrReimbursementOverAssets": { "xbrltype": "percentItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "FeeWaiverOrReimbursementOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_NetExpensesOverAssets", "weight": 1.0, "order": 2.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Fee Waiver or Reimbursement", "negatedLabel": "Fee Waiver or Reimbursement" } } }, "auth_ref": [ "r25" ] }, "oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "FeeWaiverOrReimbursementOverAssetsDateOfTermination", "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Fee Waiver or Reimbursement over Assets, Date of Termination" } } }, "auth_ref": [ "r25" ] }, "nmsf_ForeignCurrencyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ForeignCurrencyRiskMember", "presentation": [ "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Foreign Currency Risk [Member]" } } }, "auth_ref": [] }, "nmsf_ForeignInvestingRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ForeignInvestingRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Foreign Investing Risk [Member]" } } }, "auth_ref": [] }, "oef_FormN1aAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "FormN1aAbstract", "lang": { "en-us": { "role": { "label": "Form N-1A:" } } }, "auth_ref": [ "r1" ] }, "nmsf_ForwardForeignCurrencyExchangeContractsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ForwardForeignCurrencyExchangeContractsRiskMember", "presentation": [ "http://www.northwesternmutual.com/23/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Forward Foreign Currency Exchange Contracts Risk [Member]" } } }, "auth_ref": [] }, "nmsf_FundofFundsInvestingRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "FundofFundsInvestingRiskMember", "presentation": [ "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Fund of Funds Investing Risk [Member]" } } }, "auth_ref": [] }, "nmsf_GeographicFocusRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "GeographicFocusRiskMember", "presentation": [ "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Geographic Focus Risk [Member]" } } }, "auth_ref": [] }, "nmsf_HighPortfolioTurnoverRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "HighPortfolioTurnoverRiskMember", "presentation": [ "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "High Portfolio Turnover Risk [Member]" } } }, "auth_ref": [] }, "nmsf_HighYieldDebtRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "HighYieldDebtRiskMember", "presentation": [ "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "High Yield Debt Risk [Member]" } } }, "auth_ref": [] }, "oef_HighestQuarterlyReturnLabel": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "HighestQuarterlyReturnLabel", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Highest Quarterly Return, Label [Optional Text]" } } }, "auth_ref": [ "r43" ] }, "nmsf_IncomeRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "IncomeRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Income Risk [Member]" } } }, "auth_ref": [] }, "oef_IndexNoDeductionForFeesExpensesTaxes": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "IndexNoDeductionForFeesExpensesTaxes", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Index No Deduction for Fees, Expenses, or Taxes [Text]" } } }, "auth_ref": [ "r47" ] }, "nmsf_IndexingStrategyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "IndexingStrategyRiskMember", "presentation": [ "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Indexing Strategy Risk [Member]" } } }, "auth_ref": [] }, "nmsf_InflationRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "InflationRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Inflation Risk [Member]" } } }, "auth_ref": [] }, "us-gaap_InterestRateRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://fasb.org/us-gaap/2024", "localname": "InterestRateRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Interest Rate Risk [Member]" } } }, "auth_ref": [] }, "nmsf_InvestmentStyleRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "InvestmentStyleRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Investment Style Risk [Member]" } } }, "auth_ref": [] }, "nmsf_IssuerRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "IssuerRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Issuer Risk [Member]" } } }, "auth_ref": [] }, "nmsf_LargeCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LargeCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Large Cap Company Risk [Member]" } } }, "auth_ref": [] }, "nmsf_LargePositionRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LargePositionRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Large Position Risk [Member]" } } }, "auth_ref": [] }, "nmsf_LargeTransactionRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LargeTransactionRiskMember", "presentation": [ "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Large Transaction Risk [Member]" } } }, "auth_ref": [] }, "dei_LegalEntityAxis": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/dei/2024", "localname": "LegalEntityAxis", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Series [Axis]", "documentation": "The set of legal entities associated with a report." } } }, "auth_ref": [] }, "nmsf_LeverageRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LeverageRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Leverage Risk [Member]" } } }, "auth_ref": [] }, "nmsf_LiquidityRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LiquidityRiskMember", "presentation": [ "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Liquidity Risk [Member]" } } }, "auth_ref": [] }, "nmsf_LoanRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "LoanRiskMember", "presentation": [ "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Loan Risk [Member]" } } }, "auth_ref": [] }, "oef_LowestQuarterlyReturnLabel": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "LowestQuarterlyReturnLabel", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Lowest Quarterly Return, Label [Optional Text]" } } }, "auth_ref": [ "r43" ] }, "nmsf_MSCIAllCountryWorldexUSIndexNetMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MSCIAllCountryWorldexUSIndexNetMember", "presentation": [ "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "MSCI® All Country World (ex-US) Index (Net)(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_MSCIAllCountryWorldexUSValueIndexNetMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MSCIAllCountryWorldexUSValueIndexNetMember", "presentation": [ "http://www.northwesternmutual.com/17/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "MSCI® All Country World (ex-US) Value Index (Net)(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_MSCIEAFEGrowthIndexNetMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MSCIEAFEGrowthIndexNetMember", "presentation": [ "http://www.northwesternmutual.com/15/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "MSCI EAFE® Growth Index (Net)(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_MSCIEAFEIndexNetMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MSCIEAFEIndexNetMember", "presentation": [ "http://www.northwesternmutual.com/16/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "MSCI EAFE® Index (Net)(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_MSCIEmergingMarketsIndexNetMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MSCIEmergingMarketsIndexNetMember", "presentation": [ "http://www.northwesternmutual.com/18/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "MSCI® Emerging Markets Index (Net)(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "oef_ManagementFeesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ManagementFeesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_ExpensesOverAssets", "weight": 1.0, "order": 1.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Management Fees (as a percentage of Assets)" } } }, "auth_ref": [ "r17" ] }, "oef_MarketIndexPerformanceTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MarketIndexPerformanceTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Market Index Performance [Table]" } } }, "auth_ref": [ "r47" ] }, "nmsf_MarketRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MarketRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Market Risk [Member]" } } }, "auth_ref": [] }, "oef_MaximumAccountFee": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumAccountFee", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Account Fee" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumAccountFeeOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumAccountFeeOverAssets", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Account Fee (as a percentage of Assets)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumCumulativeSalesChargeOverOfferingPrice": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumCumulativeSalesChargeOverOfferingPrice", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Cumulative Sales Charge (as a percentage of Offering Price)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumCumulativeSalesChargeOverOther": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumCumulativeSalesChargeOverOther", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Cumulative Sales Charge (as a percentage)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumDeferredSalesChargeOverOfferingPrice": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumDeferredSalesChargeOverOfferingPrice", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Deferred Sales Charge (as a percentage of Offering Price)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumDeferredSalesChargeOverOther": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumDeferredSalesChargeOverOther", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Deferred Sales Charge (as a percentage)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumSalesChargeImposedOnPurchasesOverOfferingPrice", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)" } } }, "auth_ref": [ "r12" ] }, "oef_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage)" } } }, "auth_ref": [ "r12" ] }, "nmsf_MicroCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MicroCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Micro Cap Company Risk [Member]" } } }, "auth_ref": [] }, "nmsf_MidCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MidCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Mid Cap Company Risk [Member]" } } }, "auth_ref": [] }, "nmsf_MidandSmallCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MidandSmallCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/2/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Mid and Small Cap Company Risk [Member]" } } }, "auth_ref": [] }, "oef_MoneyMarketSevenDayTaxEquivalentYield": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MoneyMarketSevenDayTaxEquivalentYield", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Money Market Seven Day Tax Equivalent Yield" } } }, "auth_ref": [ "r50" ] }, "oef_MoneyMarketSevenDayYield": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MoneyMarketSevenDayYield", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Money Market Seven Day Yield" } } }, "auth_ref": [ "r50" ] }, "oef_MoneyMarketSevenDayYieldCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MoneyMarketSevenDayYieldCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Money Market Seven Day Yield, Caption [Optional Text]" } } }, "auth_ref": [ "r50" ] }, "oef_MoneyMarketSevenDayYieldColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MoneyMarketSevenDayYieldColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Money Market Seven Day Yield Column [Optional Text]" } } }, "auth_ref": [ "r50" ] }, "oef_MoneyMarketSevenDayYieldPhone": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "MoneyMarketSevenDayYieldPhone", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Money Market Seven Day Yield Phone" } } }, "auth_ref": [ "r51" ] }, "nmsf_MortgageandAssetBackedSecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MortgageandAssetBackedSecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Mortgage-and Asset-Backed Securities Risk [Member]" } } }, "auth_ref": [] }, "nmsf_MunicipalSecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "MunicipalSecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Municipal Securities Risk [Member]" } } }, "auth_ref": [] }, "oef_NetExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "NetExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": null, "weight": null, "order": null, "root": true } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Net Expenses (as a percentage of Assets)", "totalLabel": "Net Expenses" } } }, "auth_ref": [ "r16" ] }, "oef_ObjectiveHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ObjectiveHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://xbrl.sec.gov/rr/role/RiskReturn" ], "lang": { "en-us": { "role": { "label": "Objective [Heading]" } } }, "auth_ref": [ "r5" ] }, "oef_ObjectivePrimaryTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ObjectivePrimaryTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://xbrl.sec.gov/rr/role/RiskReturn" ], "lang": { "en-us": { "role": { "label": "Objective, Primary [Text Block]" } } }, "auth_ref": [ "r5" ] }, "oef_ObjectiveSecondaryTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ObjectiveSecondaryTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://xbrl.sec.gov/rr/role/RiskReturn" ], "lang": { "en-us": { "role": { "label": "Objective, Secondary [Text Block]" } } }, "auth_ref": [ "r5" ] }, "nmsf_OneThirdEachThreeIndexesMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "OneThirdEachThreeIndexesMember", "presentation": [ "http://www.northwesternmutual.com/25/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "1/3 each: Bloomberg® Global Aggregate — Credit Component ex Emerging Markets, Hedged USD; ICE BofA® Global High Yield BB-B Rated Constrained Developed Markets Index, Hedged USD; JP Morgan® EMBI Global(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "oef_OperatingExpensesCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "OperatingExpensesCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Operating Expenses Caption [Optional Text]" } } }, "auth_ref": [ "r16" ] }, "oef_OperatingExpensesColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "OperatingExpensesColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Operating Expenses Column [Optional Text]" } } }, "auth_ref": [ "r16" ] }, "oef_OtherExpensesNewFundBasedOnEstimates": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "OtherExpensesNewFundBasedOnEstimates", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Other Expenses, New Fund, Based on Estimates [Text]" } } }, "auth_ref": [ "r32" ] }, "oef_OtherExpensesOverAssets": { "xbrltype": "nonNegativePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "OtherExpensesOverAssets", "calculation": { "http://xbrl.sec.gov/rr/role/OperatingExpensesData": { "parentTag": "oef_ExpensesOverAssets", "weight": 1.0, "order": 4.0 } }, "presentation": [ "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/OperatingExpensesData" ], "lang": { "en-us": { "role": { "label": "Other Expenses (as a percentage of Assets):", "totalLabel": "Other Expenses" } } }, "auth_ref": [ "r19" ] }, "nmsf_OtherInvestmentCompaniesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "OtherInvestmentCompaniesRiskMember", "presentation": [ "http://www.northwesternmutual.com/14/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Other Investment Companies Risk [Member]" } } }, "auth_ref": [] }, "oef_PerfInceptionDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerfInceptionDate", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Performance Inception Date" } } }, "auth_ref": [ "r6" ] }, "oef_PerformanceAdditionalMarketIndex": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceAdditionalMarketIndex", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Additional Market Index [Text]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformanceAvailabilityPhone": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceAvailabilityPhone", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Availability Phone [Text]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformanceAvailabilityWebSiteAddress": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceAvailabilityWebSiteAddress", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Availability Website Address [Text]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformanceInformationIllustratesVariabilityOfReturns": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceInformationIllustratesVariabilityOfReturns", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Information Illustrates Variability of Returns [Text]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformanceMeasureAxis": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceMeasureAxis", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Performance Measure [Axis]" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceMeasureDomain": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceMeasureDomain", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Before Taxes" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Narrative [Text Block]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformanceOneYearOrLess": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceOneYearOrLess", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance One Year or Less [Text]" } } }, "auth_ref": [ "r42" ] }, "oef_PerformancePastDoesNotIndicateFuture": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformancePastDoesNotIndicateFuture", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Past Does Not Indicate Future [Text]" } } }, "auth_ref": [ "r7", "r42" ] }, "oef_PerformanceTableClosingTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableClosingTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Closing [Text Block]" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceTableDoesReflectSalesLoads": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableDoesReflectSalesLoads", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Does Reflect Sales Loads" } } }, "auth_ref": [ "r52" ] }, "oef_PerformanceTableExplanationAfterTaxHigher": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableExplanationAfterTaxHigher", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Explanation after Tax Higher" } } }, "auth_ref": [ "r57" ] }, "oef_PerformanceTableFootnotesReasonPerformanceInformationForClassDifferentFromImmediatelyPrecedingPeriod": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableFootnotesReasonPerformanceInformationForClassDifferentFromImmediatelyPrecedingPeriod", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text]" } } }, "auth_ref": [ "r49" ] }, "oef_PerformanceTableFootnotesTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableFootnotesTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Footnotes" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceTableHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Heading" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceTableMarketIndexChanged": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableMarketIndexChanged", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Market Index Changed" } } }, "auth_ref": [ "r54" ] }, "oef_PerformanceTableNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Narrative" } } }, "auth_ref": [ "r52" ] }, "oef_PerformanceTableNotRelevantToTaxDeferred": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableNotRelevantToTaxDeferred", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Not Relevant to Tax Deferred" } } }, "auth_ref": [ "r56" ] }, "oef_PerformanceTableOneClassOfAfterTaxShown": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableOneClassOfAfterTaxShown", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table One Class of after Tax Shown [Text]" } } }, "auth_ref": [ "r47", "r53" ] }, "oef_PerformanceTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance [Table]" } } }, "auth_ref": [ "r47" ] }, "oef_PerformanceTableUsesHighestFederalRate": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PerformanceTableUsesHighestFederalRate", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Performance Table Uses Highest Federal Rate" } } }, "auth_ref": [ "r55" ] }, "oef_PortfolioTurnoverHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PortfolioTurnoverHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Portfolio Turnover [Heading]" } } }, "auth_ref": [ "r31" ] }, "oef_PortfolioTurnoverRate": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PortfolioTurnoverRate", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Portfolio Turnover, Rate" } } }, "auth_ref": [ "r9", "r31" ] }, "oef_PortfolioTurnoverTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "PortfolioTurnoverTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Portfolio Turnover [Text Block]" } } }, "auth_ref": [ "r31" ] }, "nmsf_PreferredStocksRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "PreferredStocksRiskMember", "presentation": [ "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Preferred Stocks Risk [Member]" } } }, "auth_ref": [] }, "nmsf_PrepaymentandExtensionRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "PrepaymentandExtensionRiskMember", "presentation": [ "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Prepayment and Extension Risk [Member]" } } }, "auth_ref": [] }, "oef_ProspectusDate": { "xbrltype": "dateItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ProspectusDate", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Prospectus Date" } } }, "auth_ref": [ "r4" ] }, "oef_ProspectusLineItems": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ProspectusLineItems", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/N1aCover", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/N1aCover", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Prospectus [Line Items]" } } }, "auth_ref": [ "r2" ] }, "oef_ProspectusTable": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ProspectusTable", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/N1aCover", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/N1aCover", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/RiskReturn", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Prospectus [Table]" } } }, "auth_ref": [ "r2" ] }, "nmsf_REITsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "REITsRiskMember", "presentation": [ "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "REITs Risk [Member]" } } }, "auth_ref": [] }, "oef_RedemptionFee": { "xbrltype": "nonPositiveMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RedemptionFee", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Redemption Fee", "negatedLabel": "Redemption Fee" } } }, "auth_ref": [ "r12" ] }, "oef_RedemptionFeeOverRedemption": { "xbrltype": "nonPositivePure4ItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RedemptionFeeOverRedemption", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Redemption Fee (as a percentage of Amount Redeemed)", "negatedLabel": "Redemption Fee (as a percentage of Amount Redeemed)" } } }, "auth_ref": [ "r12" ] }, "nmsf_RepurchaseAgreementsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "RepurchaseAgreementsRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Repurchase Agreements Risk [Member]" } } }, "auth_ref": [] }, "oef_RiskAxis": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskAxis", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk [Axis]" } } }, "auth_ref": [ "r36" ] }, "oef_RiskLoseMoneyMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskLoseMoneyMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Lose Money [Member]" } } }, "auth_ref": [ "r35" ] }, "oef_RiskMoneyMarketFundMayImposeFeesOrSuspendSalesMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskMoneyMarketFundMayImposeFeesOrSuspendSalesMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Money Market Fund May Impose Fees or Suspend Sales [Member]" } } }, "auth_ref": [ "r37" ] }, "oef_RiskMoneyMarketFundMayNotPreserveDollarMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskMoneyMarketFundMayNotPreserveDollarMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Money Market Fund May Not Preserve Dollar [Member]" } } }, "auth_ref": [ "r37" ] }, "oef_RiskMoneyMarketFundPriceFluctuatesMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskMoneyMarketFundPriceFluctuatesMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Money Market Fund Price Fluctuates [Member]" } } }, "auth_ref": [ "r38" ] }, "oef_RiskMoneyMarketFundSponsorMayNotProvideSupportMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskMoneyMarketFundSponsorMayNotProvideSupportMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Money Market Fund Sponsor May Not Provide Support [Member]" } } }, "auth_ref": [ "r37" ] }, "oef_RiskNondiversifiedStatusMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskNondiversifiedStatusMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Nondiversified Status [Member]" } } }, "auth_ref": [ "r40" ] }, "oef_RiskNotInsuredDepositoryInstitutionMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskNotInsuredDepositoryInstitutionMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Not Insured Depository Institution [Member]" } } }, "auth_ref": [ "r39" ] }, "oef_RiskNotInsuredMember": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskNotInsuredMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk Not Insured [Member]" } } }, "auth_ref": [ "r37" ] }, "oef_RiskReturnHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskReturnHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://xbrl.sec.gov/rr/role/RiskReturn" ], "lang": { "en-us": { "role": { "label": "Risk/Return [Heading]" } } }, "auth_ref": [ "r59" ] }, "oef_RiskTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RiskTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://xbrl.sec.gov/rr/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Risk [Text Block]" } } }, "auth_ref": [ "r36" ] }, "oef_RisksAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "RisksAbstract", "lang": { "en-us": { "role": { "label": "Risks [Abstract]" } } }, "auth_ref": [ "r35" ] }, "nmsf_Russell1000GrowthIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "Russell1000GrowthIndexMember", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell 1000® Growth Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_Russell1000ValueIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "Russell1000ValueIndexMember", "presentation": [ "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell 1000® Value Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_Russell2000GrowthIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "Russell2000GrowthIndexMember", "presentation": [ "http://www.northwesternmutual.com/12/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell 2000® Growth Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_Russell2000ValueIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "Russell2000ValueIndexMember", "presentation": [ "http://www.northwesternmutual.com/14/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell 2000® Value Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_RussellMidCapGrowthIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "RussellMidCapGrowthIndexMember", "presentation": [ "http://www.northwesternmutual.com/9/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell MidCap® Growth Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_RussellMidCapValueIndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "RussellMidCapValueIndexMember", "presentation": [ "http://www.northwesternmutual.com/11/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "Russell MidCap® Value Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_S000000039Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000039Member", "presentation": [ "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/RiskReturn", "http://www.northwesternmutual.com/12/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Small Cap Growth Stock Portfolio", "label": "S000000039 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000040Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000040Member", "presentation": [ "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/RiskReturn", "http://www.northwesternmutual.com/3/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Cap Core Stock Portfolio", "label": "S000000040 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000041Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000041Member", "presentation": [ "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/RiskReturn", "http://www.northwesternmutual.com/7/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Domestic Equity Portfolio", "label": "S000000041 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000042Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000042Member", "presentation": [ "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/RiskReturn", "http://www.northwesternmutual.com/8/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Equity Income Portfolio", "label": "S000000042 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000043Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000043Member", "presentation": [ "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/RiskReturn", "http://www.northwesternmutual.com/5/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 500 Stock Portfolio", "label": "S000000043 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000044Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000044Member", "presentation": [ "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/RiskReturn", "http://www.northwesternmutual.com/28/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Moderate Portfolio", "label": "S000000044 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000045Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000045Member", "presentation": [ "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/RiskReturn", "http://www.northwesternmutual.com/29/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Balanced Portfolio", "label": "S000000045 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000046Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000046Member", "presentation": [ "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/RiskReturn", "http://www.northwesternmutual.com/24/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "High Yield Bond Portfolio", "label": "S000000046 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000047Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000047Member", "presentation": [ "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/RiskReturn", "http://www.northwesternmutual.com/21/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Select Bond Portfolio", "label": "S000000047 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000048Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000048Member", "presentation": [ "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/RiskReturn", "http://www.northwesternmutual.com/19/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Government Money Market Portfolio", "label": "S000000048 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000049Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000049Member", "presentation": [ "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/RiskReturn", "http://www.northwesternmutual.com/14/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Small Cap Value Portfolio", "label": "S000000049 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000050Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000050Member", "presentation": [ "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/RiskReturn", "http://www.northwesternmutual.com/9/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Mid Cap Growth Stock Portfolio", "label": "S000000050 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000051Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000051Member", "presentation": [ "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/RiskReturn", "http://www.northwesternmutual.com/15/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "International Growth Portfolio", "label": "S000000051 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000052Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000052Member", "presentation": [ "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/RiskReturn", "http://www.northwesternmutual.com/17/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "International Equity Portfolio", "label": "S000000052 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000053Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000053Member", "presentation": [ "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/RiskReturn", "http://www.northwesternmutual.com/11/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Mid Cap Value Portfolio", "label": "S000000053 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000054Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000054Member", "presentation": [ "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/RiskReturn", "http://www.northwesternmutual.com/10/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 400 Stock Portfolio", "label": "S000000054 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000055Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000055Member", "presentation": [ "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/RiskReturn", "http://www.northwesternmutual.com/2/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Focused Appreciation Portfolio", "label": "S000000055 [Member]" } } }, "auth_ref": [] }, "nmsf_S000000056Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000000056Member", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/RiskReturn", "http://www.northwesternmutual.com/1/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Growth Stock Portfolio", "label": "S000000056 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018227Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018227Member", "presentation": [ "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/RiskReturn", "http://www.northwesternmutual.com/6/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Company Value Portfolio", "label": "S000018227 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018228Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018228Member", "presentation": [ "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/RiskReturn", "http://www.northwesternmutual.com/23/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Inflation Managed Portfolio", "label": "S000018228 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018229Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018229Member", "presentation": [ "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/RiskReturn", "http://www.northwesternmutual.com/4/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Large Cap Blend Portfolio", "label": "S000018229 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018230Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018230Member", "presentation": [ "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/RiskReturn", "http://www.northwesternmutual.com/16/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Research International Core Portfolio", "label": "S000018230 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018231Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018231Member", "presentation": [ "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/RiskReturn", "http://www.northwesternmutual.com/13/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Index 600 Stock Portfolio", "label": "S000018231 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018232Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018232Member", "presentation": [ "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/RiskReturn", "http://www.northwesternmutual.com/18/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Emerging Markets Equity Portfolio", "label": "S000018232 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018233Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018233Member", "presentation": [ "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/RiskReturn", "http://www.northwesternmutual.com/20/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Short-Term Bond Portfolio", "label": "S000018233 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018234Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018234Member", "presentation": [ "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/RiskReturn", "http://www.northwesternmutual.com/22/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Long-Term US Government Bond Portfolio", "label": "S000018234 [Member]" } } }, "auth_ref": [] }, "nmsf_S000018235Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000018235Member", "presentation": [ "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/RiskReturn", "http://www.northwesternmutual.com/25/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Multi-Sector Bond Portfolio", "label": "S000018235 [Member]" } } }, "auth_ref": [] }, "nmsf_S000091982Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000091982Member", "presentation": [ "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/RiskReturn", "http://www.northwesternmutual.com/30/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Conservative Portfolio", "label": "S000091982 [Member]" } } }, "auth_ref": [] }, "nmsf_S000091983Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000091983Member", "presentation": [ "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/RiskReturn", "http://www.northwesternmutual.com/27/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Aggressive Portfolio", "label": "S000091983 [Member]" } } }, "auth_ref": [] }, "nmsf_S000091984Member": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "S000091984Member", "presentation": [ "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/RiskReturn", "http://www.northwesternmutual.com/26/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "verboseLabel": "Active Passive Very Aggressive Portfolio", "label": "S000091984 [Member]" } } }, "auth_ref": [] }, "nmsf_SP500IndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SP500IndexMember", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "S&P 500® Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_SPMidCap400IndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SPMidCap400IndexMember", "presentation": [ "http://www.northwesternmutual.com/10/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "S&P MidCap 400® Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_SPSmallCap600IndexMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SPSmallCap600IndexMember", "presentation": [ "http://www.northwesternmutual.com/13/role/PerformanceTableData" ], "lang": { "en-us": { "role": { "label": "S&P SmallCap 600® Index(reflects no deduction for fees, expenses or taxes)[Member]" } } }, "auth_ref": [] }, "nmsf_SectorFocusRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SectorFocusRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Sector Focus Risk [Member]" } } }, "auth_ref": [] }, "nmsf_SecurityFocusRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SecurityFocusRiskMember", "presentation": [ "http://www.northwesternmutual.com/6/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Security Focus Risk [Member]" } } }, "auth_ref": [] }, "oef_ShareClassDomain": { "xbrltype": "domainItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareClassDomain", "presentation": [ "http://www.northwesternmutual.com/1/role/BarChartData", "http://www.northwesternmutual.com/1/role/ExpenseExample", "http://www.northwesternmutual.com/1/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/1/role/OperatingExpensesData", "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/1/role/PerformanceTableData", "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/BarChartData", "http://www.northwesternmutual.com/10/role/ExpenseExample", "http://www.northwesternmutual.com/10/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/10/role/OperatingExpensesData", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceTableData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/BarChartData", "http://www.northwesternmutual.com/11/role/ExpenseExample", "http://www.northwesternmutual.com/11/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/11/role/OperatingExpensesData", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceTableData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/BarChartData", "http://www.northwesternmutual.com/12/role/ExpenseExample", "http://www.northwesternmutual.com/12/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/12/role/OperatingExpensesData", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceTableData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/BarChartData", "http://www.northwesternmutual.com/13/role/ExpenseExample", "http://www.northwesternmutual.com/13/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/13/role/OperatingExpensesData", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceTableData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/BarChartData", "http://www.northwesternmutual.com/14/role/ExpenseExample", "http://www.northwesternmutual.com/14/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/14/role/OperatingExpensesData", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceTableData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/BarChartData", "http://www.northwesternmutual.com/15/role/ExpenseExample", "http://www.northwesternmutual.com/15/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/15/role/OperatingExpensesData", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceTableData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/BarChartData", "http://www.northwesternmutual.com/16/role/ExpenseExample", "http://www.northwesternmutual.com/16/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/16/role/OperatingExpensesData", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceTableData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/BarChartData", "http://www.northwesternmutual.com/17/role/ExpenseExample", "http://www.northwesternmutual.com/17/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/17/role/OperatingExpensesData", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceTableData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/BarChartData", "http://www.northwesternmutual.com/18/role/ExpenseExample", "http://www.northwesternmutual.com/18/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/18/role/OperatingExpensesData", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceTableData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/BarChartData", "http://www.northwesternmutual.com/19/role/ExpenseExample", "http://www.northwesternmutual.com/19/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/19/role/OperatingExpensesData", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceTableData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/BarChartData", "http://www.northwesternmutual.com/2/role/ExpenseExample", "http://www.northwesternmutual.com/2/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/2/role/OperatingExpensesData", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceTableData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/BarChartData", "http://www.northwesternmutual.com/20/role/ExpenseExample", "http://www.northwesternmutual.com/20/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/20/role/OperatingExpensesData", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceTableData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/BarChartData", "http://www.northwesternmutual.com/21/role/ExpenseExample", "http://www.northwesternmutual.com/21/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/21/role/OperatingExpensesData", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceTableData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/BarChartData", "http://www.northwesternmutual.com/22/role/ExpenseExample", "http://www.northwesternmutual.com/22/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/22/role/OperatingExpensesData", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceTableData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/BarChartData", "http://www.northwesternmutual.com/23/role/ExpenseExample", "http://www.northwesternmutual.com/23/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/23/role/OperatingExpensesData", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceTableData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/BarChartData", "http://www.northwesternmutual.com/24/role/ExpenseExample", "http://www.northwesternmutual.com/24/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/24/role/OperatingExpensesData", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceTableData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/BarChartData", "http://www.northwesternmutual.com/25/role/ExpenseExample", "http://www.northwesternmutual.com/25/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/25/role/OperatingExpensesData", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceTableData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/BarChartData", "http://www.northwesternmutual.com/26/role/ExpenseExample", "http://www.northwesternmutual.com/26/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/26/role/OperatingExpensesData", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceTableData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/BarChartData", "http://www.northwesternmutual.com/27/role/ExpenseExample", "http://www.northwesternmutual.com/27/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/27/role/OperatingExpensesData", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceTableData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/BarChartData", "http://www.northwesternmutual.com/28/role/ExpenseExample", "http://www.northwesternmutual.com/28/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/28/role/OperatingExpensesData", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceTableData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/BarChartData", "http://www.northwesternmutual.com/29/role/ExpenseExample", "http://www.northwesternmutual.com/29/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/29/role/OperatingExpensesData", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceTableData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/BarChartData", "http://www.northwesternmutual.com/3/role/ExpenseExample", "http://www.northwesternmutual.com/3/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/3/role/OperatingExpensesData", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceTableData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/BarChartData", "http://www.northwesternmutual.com/30/role/ExpenseExample", "http://www.northwesternmutual.com/30/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/30/role/OperatingExpensesData", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceTableData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/BarChartData", "http://www.northwesternmutual.com/4/role/ExpenseExample", "http://www.northwesternmutual.com/4/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/4/role/OperatingExpensesData", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceTableData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/BarChartData", "http://www.northwesternmutual.com/5/role/ExpenseExample", "http://www.northwesternmutual.com/5/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/5/role/OperatingExpensesData", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceTableData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/BarChartData", "http://www.northwesternmutual.com/6/role/ExpenseExample", "http://www.northwesternmutual.com/6/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/6/role/OperatingExpensesData", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceTableData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/BarChartData", "http://www.northwesternmutual.com/7/role/ExpenseExample", "http://www.northwesternmutual.com/7/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/7/role/OperatingExpensesData", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceTableData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/BarChartData", "http://www.northwesternmutual.com/8/role/ExpenseExample", "http://www.northwesternmutual.com/8/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/8/role/OperatingExpensesData", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceTableData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/BarChartData", "http://www.northwesternmutual.com/9/role/ExpenseExample", "http://www.northwesternmutual.com/9/role/ExpenseExampleNoRedemption", "http://www.northwesternmutual.com/9/role/OperatingExpensesData", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceTableData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/BarChartData", "http://xbrl.sec.gov/rr/role/ExpenseExample", "http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption", "http://xbrl.sec.gov/rr/role/OperatingExpensesData", "http://xbrl.sec.gov/rr/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceTableData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Share Classes" } } }, "auth_ref": [ "r3" ] }, "oef_ShareholderFeeOther": { "xbrltype": "nonNegativeMonetaryItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareholderFeeOther", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Shareholder Fee, Other" } } }, "auth_ref": [ "r12" ] }, "oef_ShareholderFeesAbstract": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareholderFeesAbstract", "lang": { "en-us": { "role": { "label": "Shareholder Fees:" } } }, "auth_ref": [ "r12" ] }, "oef_ShareholderFeesCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareholderFeesCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Shareholder Fees Caption [Optional Text]" } } }, "auth_ref": [ "r12" ] }, "oef_ShareholderFeesColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareholderFeesColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/ShareholderFeesData", "http://www.northwesternmutual.com/10/role/ShareholderFeesData", "http://www.northwesternmutual.com/11/role/ShareholderFeesData", "http://www.northwesternmutual.com/12/role/ShareholderFeesData", "http://www.northwesternmutual.com/13/role/ShareholderFeesData", "http://www.northwesternmutual.com/14/role/ShareholderFeesData", "http://www.northwesternmutual.com/15/role/ShareholderFeesData", "http://www.northwesternmutual.com/16/role/ShareholderFeesData", "http://www.northwesternmutual.com/17/role/ShareholderFeesData", "http://www.northwesternmutual.com/18/role/ShareholderFeesData", "http://www.northwesternmutual.com/19/role/ShareholderFeesData", "http://www.northwesternmutual.com/2/role/ShareholderFeesData", "http://www.northwesternmutual.com/20/role/ShareholderFeesData", "http://www.northwesternmutual.com/21/role/ShareholderFeesData", "http://www.northwesternmutual.com/22/role/ShareholderFeesData", "http://www.northwesternmutual.com/23/role/ShareholderFeesData", "http://www.northwesternmutual.com/24/role/ShareholderFeesData", "http://www.northwesternmutual.com/25/role/ShareholderFeesData", "http://www.northwesternmutual.com/26/role/ShareholderFeesData", "http://www.northwesternmutual.com/27/role/ShareholderFeesData", "http://www.northwesternmutual.com/28/role/ShareholderFeesData", "http://www.northwesternmutual.com/29/role/ShareholderFeesData", "http://www.northwesternmutual.com/3/role/ShareholderFeesData", "http://www.northwesternmutual.com/30/role/ShareholderFeesData", "http://www.northwesternmutual.com/4/role/ShareholderFeesData", "http://www.northwesternmutual.com/5/role/ShareholderFeesData", "http://www.northwesternmutual.com/6/role/ShareholderFeesData", "http://www.northwesternmutual.com/7/role/ShareholderFeesData", "http://www.northwesternmutual.com/8/role/ShareholderFeesData", "http://www.northwesternmutual.com/9/role/ShareholderFeesData", "http://xbrl.sec.gov/rr/role/ShareholderFeesData" ], "lang": { "en-us": { "role": { "label": "Shareholder Fees Column [Optional Text]" } } }, "auth_ref": [ "r12" ] }, "oef_ShareholderFeesTableTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ShareholderFeesTableTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/FeesAndExpenses", "http://www.northwesternmutual.com/10/role/FeesAndExpenses", "http://www.northwesternmutual.com/11/role/FeesAndExpenses", "http://www.northwesternmutual.com/12/role/FeesAndExpenses", "http://www.northwesternmutual.com/13/role/FeesAndExpenses", "http://www.northwesternmutual.com/14/role/FeesAndExpenses", "http://www.northwesternmutual.com/15/role/FeesAndExpenses", "http://www.northwesternmutual.com/16/role/FeesAndExpenses", "http://www.northwesternmutual.com/17/role/FeesAndExpenses", "http://www.northwesternmutual.com/18/role/FeesAndExpenses", "http://www.northwesternmutual.com/19/role/FeesAndExpenses", "http://www.northwesternmutual.com/2/role/FeesAndExpenses", "http://www.northwesternmutual.com/20/role/FeesAndExpenses", "http://www.northwesternmutual.com/21/role/FeesAndExpenses", "http://www.northwesternmutual.com/22/role/FeesAndExpenses", "http://www.northwesternmutual.com/23/role/FeesAndExpenses", "http://www.northwesternmutual.com/24/role/FeesAndExpenses", "http://www.northwesternmutual.com/25/role/FeesAndExpenses", "http://www.northwesternmutual.com/26/role/FeesAndExpenses", "http://www.northwesternmutual.com/27/role/FeesAndExpenses", "http://www.northwesternmutual.com/28/role/FeesAndExpenses", "http://www.northwesternmutual.com/29/role/FeesAndExpenses", "http://www.northwesternmutual.com/3/role/FeesAndExpenses", "http://www.northwesternmutual.com/30/role/FeesAndExpenses", "http://www.northwesternmutual.com/4/role/FeesAndExpenses", "http://www.northwesternmutual.com/5/role/FeesAndExpenses", "http://www.northwesternmutual.com/6/role/FeesAndExpenses", "http://www.northwesternmutual.com/7/role/FeesAndExpenses", "http://www.northwesternmutual.com/8/role/FeesAndExpenses", "http://www.northwesternmutual.com/9/role/FeesAndExpenses", "http://xbrl.sec.gov/rr/role/FeesAndExpenses" ], "lang": { "en-us": { "role": { "label": "Shareholder Fees [Table]" } } }, "auth_ref": [ "r12" ] }, "nmsf_ShortSaleRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "ShortSaleRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Short Sale Risk [Member]" } } }, "auth_ref": [] }, "nmsf_SmallCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SmallCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Small Cap Company Risk [Member]" } } }, "auth_ref": [] }, "nmsf_SmallandMidCapCompanyRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "SmallandMidCapCompanyRiskMember", "presentation": [ "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/26/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Small and Mid Cap Company Risk [Member]" } } }, "auth_ref": [] }, "nmsf_StableNetAssetValueRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "StableNetAssetValueRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Stable Net Asset Value Risk [Member]" } } }, "auth_ref": [] }, "oef_StrategyHeading": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "StrategyHeading", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/InvestmentStrategy" ], "lang": { "en-us": { "role": { "label": "Strategy [Heading]" } } }, "auth_ref": [ "r34" ] }, "oef_StrategyNarrativeTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "StrategyNarrativeTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/InvestmentStrategy" ], "lang": { "en-us": { "role": { "label": "Strategy Narrative [Text Block]" } } }, "auth_ref": [ "r34" ] }, "oef_StrategyPortfolioConcentration": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "StrategyPortfolioConcentration", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentStrategy", "http://www.northwesternmutual.com/10/role/InvestmentStrategy", "http://www.northwesternmutual.com/11/role/InvestmentStrategy", "http://www.northwesternmutual.com/12/role/InvestmentStrategy", "http://www.northwesternmutual.com/13/role/InvestmentStrategy", "http://www.northwesternmutual.com/14/role/InvestmentStrategy", "http://www.northwesternmutual.com/15/role/InvestmentStrategy", "http://www.northwesternmutual.com/16/role/InvestmentStrategy", "http://www.northwesternmutual.com/17/role/InvestmentStrategy", "http://www.northwesternmutual.com/18/role/InvestmentStrategy", "http://www.northwesternmutual.com/19/role/InvestmentStrategy", "http://www.northwesternmutual.com/2/role/InvestmentStrategy", "http://www.northwesternmutual.com/20/role/InvestmentStrategy", "http://www.northwesternmutual.com/21/role/InvestmentStrategy", "http://www.northwesternmutual.com/22/role/InvestmentStrategy", "http://www.northwesternmutual.com/23/role/InvestmentStrategy", "http://www.northwesternmutual.com/24/role/InvestmentStrategy", "http://www.northwesternmutual.com/25/role/InvestmentStrategy", "http://www.northwesternmutual.com/26/role/InvestmentStrategy", "http://www.northwesternmutual.com/27/role/InvestmentStrategy", "http://www.northwesternmutual.com/28/role/InvestmentStrategy", "http://www.northwesternmutual.com/29/role/InvestmentStrategy", "http://www.northwesternmutual.com/3/role/InvestmentStrategy", "http://www.northwesternmutual.com/30/role/InvestmentStrategy", "http://www.northwesternmutual.com/4/role/InvestmentStrategy", "http://www.northwesternmutual.com/5/role/InvestmentStrategy", "http://www.northwesternmutual.com/6/role/InvestmentStrategy", "http://www.northwesternmutual.com/7/role/InvestmentStrategy", "http://www.northwesternmutual.com/8/role/InvestmentStrategy", "http://www.northwesternmutual.com/9/role/InvestmentStrategy", "http://xbrl.sec.gov/rr/role/InvestmentStrategy" ], "lang": { "en-us": { "role": { "label": "Strategy Portfolio Concentration [Text]" } } }, "auth_ref": [ "r34" ] }, "oef_SupplementToProspectusTextBlock": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "SupplementToProspectusTextBlock", "presentation": [ "http://www.northwesternmutual.com/1/role/N1aCover", "http://www.northwesternmutual.com/10/role/N1aCover", "http://www.northwesternmutual.com/11/role/N1aCover", "http://www.northwesternmutual.com/12/role/N1aCover", "http://www.northwesternmutual.com/13/role/N1aCover", "http://www.northwesternmutual.com/14/role/N1aCover", "http://www.northwesternmutual.com/15/role/N1aCover", "http://www.northwesternmutual.com/16/role/N1aCover", "http://www.northwesternmutual.com/17/role/N1aCover", "http://www.northwesternmutual.com/18/role/N1aCover", "http://www.northwesternmutual.com/19/role/N1aCover", "http://www.northwesternmutual.com/2/role/N1aCover", "http://www.northwesternmutual.com/20/role/N1aCover", "http://www.northwesternmutual.com/21/role/N1aCover", "http://www.northwesternmutual.com/22/role/N1aCover", "http://www.northwesternmutual.com/23/role/N1aCover", "http://www.northwesternmutual.com/24/role/N1aCover", "http://www.northwesternmutual.com/25/role/N1aCover", "http://www.northwesternmutual.com/26/role/N1aCover", "http://www.northwesternmutual.com/27/role/N1aCover", "http://www.northwesternmutual.com/28/role/N1aCover", "http://www.northwesternmutual.com/29/role/N1aCover", "http://www.northwesternmutual.com/3/role/N1aCover", "http://www.northwesternmutual.com/30/role/N1aCover", "http://www.northwesternmutual.com/4/role/N1aCover", "http://www.northwesternmutual.com/5/role/N1aCover", "http://www.northwesternmutual.com/6/role/N1aCover", "http://www.northwesternmutual.com/7/role/N1aCover", "http://www.northwesternmutual.com/8/role/N1aCover", "http://www.northwesternmutual.com/9/role/N1aCover", "http://xbrl.sec.gov/rr/role/N1aCover" ], "lang": { "en-us": { "role": { "label": "Supplement to Prospectus [Text Block]" } } }, "auth_ref": [ "r1" ] }, "oef_ThirtyDayTaxEquivalentYield": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ThirtyDayTaxEquivalentYield", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Thirty Day Tax Equivalent Yield" } } }, "auth_ref": [ "r51" ] }, "oef_ThirtyDayYield": { "xbrltype": "pureItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ThirtyDayYield", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Thirty Day Yield" } } }, "auth_ref": [ "r51" ] }, "oef_ThirtyDayYieldCaption": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ThirtyDayYieldCaption", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Thirty Day Yield Caption [Optional Text]" } } }, "auth_ref": [ "r51" ] }, "oef_ThirtyDayYieldColumnName": { "xbrltype": "textBlockItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ThirtyDayYieldColumnName", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Thirty Day Yield Column [Optional Text]" } } }, "auth_ref": [ "r51" ] }, "oef_ThirtyDayYieldPhone": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "ThirtyDayYieldPhone", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Thirty Day Yield Phone" } } }, "auth_ref": [ "r51" ] }, "nmsf_TrackingErrorRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "TrackingErrorRiskMember", "presentation": [ "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Tracking Error Risk [Member]" } } }, "auth_ref": [] }, "nmsf_TreasuryObligationsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "TreasuryObligationsRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Treasury Obligations Risk [Member]" } } }, "auth_ref": [] }, "nmsf_USGovernmentObligationsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "USGovernmentObligationsRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "U.S. Government Obligations Risk [Member]" } } }, "auth_ref": [] }, "nmsf_USGovernmentSecuritiesRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "USGovernmentSecuritiesRiskMember", "presentation": [ "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/27/role/InvestmentRisks", "http://www.northwesternmutual.com/28/role/InvestmentRisks", "http://www.northwesternmutual.com/29/role/InvestmentRisks", "http://www.northwesternmutual.com/30/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "U.S. Government Securities Risk [Member]" } } }, "auth_ref": [] }, "nmsf_UnderlyingPortfolioRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "UnderlyingPortfolioRiskMember", "presentation": [ "http://www.northwesternmutual.com/1/role/InvestmentRisks", "http://www.northwesternmutual.com/10/role/InvestmentRisks", "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/12/role/InvestmentRisks", "http://www.northwesternmutual.com/13/role/InvestmentRisks", "http://www.northwesternmutual.com/14/role/InvestmentRisks", "http://www.northwesternmutual.com/15/role/InvestmentRisks", "http://www.northwesternmutual.com/16/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/18/role/InvestmentRisks", "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/2/role/InvestmentRisks", "http://www.northwesternmutual.com/20/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks", "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/23/role/InvestmentRisks", "http://www.northwesternmutual.com/24/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks", "http://www.northwesternmutual.com/3/role/InvestmentRisks", "http://www.northwesternmutual.com/4/role/InvestmentRisks", "http://www.northwesternmutual.com/5/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks", "http://www.northwesternmutual.com/7/role/InvestmentRisks", "http://www.northwesternmutual.com/8/role/InvestmentRisks", "http://www.northwesternmutual.com/9/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Underlying Portfolio Risk [Member]" } } }, "auth_ref": [] }, "nmsf_VariableandFloatingRateInstrumentRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "VariableandFloatingRateInstrumentRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Variable and Floating Rate Instrument Risk [Member]" } } }, "auth_ref": [] }, "nmsf_WarrantsInvestingRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "WarrantsInvestingRiskMember", "presentation": [ "http://www.northwesternmutual.com/11/role/InvestmentRisks", "http://www.northwesternmutual.com/17/role/InvestmentRisks", "http://www.northwesternmutual.com/6/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "Warrants Investing Risk [Member]" } } }, "auth_ref": [] }, "nmsf_WhenIssuedDelayedDeliveryandForwardCommitmentRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "WhenIssuedDelayedDeliveryandForwardCommitmentRiskMember", "presentation": [ "http://www.northwesternmutual.com/22/role/InvestmentRisks", "http://www.northwesternmutual.com/25/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "When Issued Delayed Delivery and Forward Commitment Risk [Member]" } } }, "auth_ref": [] }, "nmsf_WhenIssuedandDelayedDeliveryTransactionsRiskMember": { "xbrltype": "domainItemType", "nsuri": "http://www.northwesternmutual.com/20251231", "localname": "WhenIssuedandDelayedDeliveryTransactionsRiskMember", "presentation": [ "http://www.northwesternmutual.com/19/role/InvestmentRisks", "http://www.northwesternmutual.com/21/role/InvestmentRisks" ], "lang": { "en-us": { "role": { "label": "When-Issued and Delayed Delivery Transactions Risk [Member]" } } }, "auth_ref": [] }, "oef_YearToDateReturnLabel": { "xbrltype": "stringItemType", "nsuri": "http://xbrl.sec.gov/oef/2024q3", "localname": "YearToDateReturnLabel", "presentation": [ "http://www.northwesternmutual.com/1/role/PerformanceManagement", "http://www.northwesternmutual.com/10/role/PerformanceManagement", "http://www.northwesternmutual.com/11/role/PerformanceManagement", "http://www.northwesternmutual.com/12/role/PerformanceManagement", "http://www.northwesternmutual.com/13/role/PerformanceManagement", "http://www.northwesternmutual.com/14/role/PerformanceManagement", "http://www.northwesternmutual.com/15/role/PerformanceManagement", "http://www.northwesternmutual.com/16/role/PerformanceManagement", "http://www.northwesternmutual.com/17/role/PerformanceManagement", "http://www.northwesternmutual.com/18/role/PerformanceManagement", "http://www.northwesternmutual.com/19/role/PerformanceManagement", "http://www.northwesternmutual.com/2/role/PerformanceManagement", "http://www.northwesternmutual.com/20/role/PerformanceManagement", "http://www.northwesternmutual.com/21/role/PerformanceManagement", "http://www.northwesternmutual.com/22/role/PerformanceManagement", "http://www.northwesternmutual.com/23/role/PerformanceManagement", "http://www.northwesternmutual.com/24/role/PerformanceManagement", "http://www.northwesternmutual.com/25/role/PerformanceManagement", "http://www.northwesternmutual.com/26/role/PerformanceManagement", "http://www.northwesternmutual.com/27/role/PerformanceManagement", "http://www.northwesternmutual.com/28/role/PerformanceManagement", "http://www.northwesternmutual.com/29/role/PerformanceManagement", "http://www.northwesternmutual.com/3/role/PerformanceManagement", "http://www.northwesternmutual.com/30/role/PerformanceManagement", "http://www.northwesternmutual.com/4/role/PerformanceManagement", "http://www.northwesternmutual.com/5/role/PerformanceManagement", "http://www.northwesternmutual.com/6/role/PerformanceManagement", "http://www.northwesternmutual.com/7/role/PerformanceManagement", "http://www.northwesternmutual.com/8/role/PerformanceManagement", "http://www.northwesternmutual.com/9/role/PerformanceManagement", "http://xbrl.sec.gov/rr/role/PerformanceManagement" ], "lang": { "en-us": { "role": { "label": "Year to Date Return, Label [Optional Text]" } } }, "auth_ref": [ "r43" ] } } } }, "std_ref": { "r0": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Exchange Act", "Number": "240", "Section": "12", "Subsection": "b-2" }, "r1": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "1" }, "r2": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "1", "Subsection": "a" }, "r3": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "1", "Subsection": "a", "Paragraph": "1" }, "r4": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "1", "Subsection": "a", "Paragraph": "3" }, "r5": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "2", "Subsection": "a" }, "r6": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "27A", "Subsection": "d", "Paragraph": "2", "Subparagraph": "i" }, "r7": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "27A", "Subsection": "d", "Paragraph": "2", "Subparagraph": "iiii", "Clause": "A" }, "r8": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "27A", "Subsection": "d", "Paragraph": "2", "Subparagraph": "instruction", "Clause": "7" }, "r9": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "27A", "Subsection": "e" }, "r10": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "1" }, "r11": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "1", "Subparagraph": "b" }, "r12": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "2" }, "r13": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "2", "Subparagraph": "a", "Sentence": "i" }, "r14": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "2", "Subparagraph": "c" }, "r15": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "2", "Subparagraph": "d" }, "r16": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3" }, "r17": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "a" }, "r18": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "b" }, "r19": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "c", "Sentence": "i" }, "r20": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "c", "Sentence": "ii" }, "r21": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "c", "Sentence": "iii" }, "r22": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "d" }, "r23": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "d", "Clause": "B", "Sentence": "ii" }, "r24": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "d", "Sentence": "iii" }, "r25": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "e" }, "r26": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "f", "Sentence": "i" }, "r27": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "f", "Sentence": "vi" }, "r28": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "3", "Subparagraph": "f", "Sentence": "vii" }, "r29": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "4" }, "r30": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "4", "Subparagraph": "f" }, "r31": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "5" }, "r32": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instruction", "Paragraph": "6", "Subparagraph": "a" }, "r33": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "3", "Subsection": "instrution", "Paragraph": "3" }, "r34": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "a" }, "r35": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1" }, "r36": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1", "Subparagraph": "i", "Clause": "instruction" }, "r37": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1", "Subparagraph": "ii" }, "r38": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1", "Subparagraph": "ii", "Clause": "A" }, "r39": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1", "Subparagraph": "iii" }, "r40": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "1", "Subparagraph": "iv" }, "r41": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2" }, "r42": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "i" }, "r43": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "ii" }, "r44": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "ii", "Sentence": "instruction", "Clause": "1", "Subclause": "a" }, "r45": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "ii", "Sentence": "instruction", "Clause": "3", "Subclause": "b" }, "r46": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "ii", "Sentence": "instruction", "Clause": "3", "Subclause": "c" }, "r47": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iii" }, "r48": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "instruction", "Clause": "3" }, "r49": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "instruction", "Clause": "3", "Subclause": "c" }, "r50": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "instruction", "Clause": "a", "Sentence": "2" }, "r51": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "instruction", "Clause": "d", "Sentence": "2" }, "r52": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv" }, "r53": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv", "Clause": "C" }, "r54": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv", "Clause": "c", "Sentence": "2" }, "r55": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv", "Sentence": "A" }, "r56": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv", "Sentence": "B" }, "r57": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Form N-1A", "Section": "4", "Subsection": "b", "Paragraph": "2", "Subparagraph": "iv", "Sentence": "D" }, "r58": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Name": "Regulation S-T", "Number": "232", "Section": "313" }, "r59": { "role": "http://www.xbrl.org/2003/role/presentationRef", "Publisher": "SEC", "Section": "2", "Name": "Form N-1A", "Subsection": "a" } } }