State Street Moderately Aggressive ETF Portfolio Investment Strategy - State Street Moderately Aggressive ETF Portfolio	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Times New Roman;font-size:11.5pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	SSGA Funds Management, Inc. (“SSGA FM” or “Subadviser”), subadviser to the Portfolio, invests, under normal circumstances, at least 80% of the Portfolio’s net assets in investment companies known as exchange-traded funds (the “Underlying ETFs”), including exchange-traded funds advised by SSGA FM. The Portfolio allocates its assets among various asset classes. SSGA FM establishes specific investment percentages for the asset classes and then selects the Underlying ETFs in which the Portfolio invests. The Portfolio invests a significant portion of its assets in Underlying ETFs that invest primarily in the U.S. and international equity markets with moderate allocations to Underlying ETFs that invest primarily in fixed income securities in an effort to reduce portfolio volatility in difficult market environments. In an effort to achieve its investment objectives and reduce portfolio volatility over an intermediate-term cycle, equity investments are allocated across a range of asset classes, which can include, but are not limited to, varying market capitalization categories (large, mid and small), U.S. and foreign real estate investment trust (“REIT”), and foreign developed and emerging markets, and the Portfolio’s fixed income investments may be allocated across a range of sectors which can include, but are not limited to, government, inflation protected government (both U.S. Treasury Inflation Protected Securities (“TIPS”) and equivalent foreign securities), bank loans, and U.S. and foreign debt securities, including emerging market debt securities, as well as investment grade corporate debt securities and lower rated, higher-yielding debt securities (commonly referred to as “junk bonds”). In addition, the Portfolio may invest in other asset classes (e.g., commodities) through exchange traded investment vehicles. The following chart describes the strategic target allocations, as of April 27, 2026, among the range of equities, fixed income and cash/money market securities for the Portfolio. You should note that these target allocations may not directly correspond to investment in the Underlying ETFs because each Underlying ETF may contain various subsets of an asset class (e.g., large cap and mid cap equity securities), and the target allocations are subject to review and modification by SSGA FM. In addition to investing in Underlying ETFs, the Portfolio may invest in other exchange traded vehicles such as exchange traded notes and exchange traded grantor trusts.Asset ClassTarget AllocationEquities80%U.S. Large Cap35%U.S. Mid Cap4.5%U.S. Small Cap4.5%International Equity18.5%International Small Cap3%Emerging Market Equity9.5%Real Estate Investment Trusts1%International Real Estate Investment Trusts1%Commodities3%Fixed Income18%U.S. Fixed Income13.5%High Yield1.5%Bank Loans1.5%Emerging Market Debt1.5%Treasury Inflation-Protected Securities0%Cash/Cash Equivalents2%Individual figures may not add up to the totals shown due to rounding. Although the Portfolio will invest new assets and reinvest dividends based on the target allocations at such time, the Portfolio’s target allocations could change substantially over time as the Underlying ETFs’ asset values change due to market movements and portfolio management decisions. The Portfolio currently seeks to achieve capital growth through its investments in Underlying ETFs that invest primarily in equity securities of large U.S. and foreign companies. The Portfolio currently seeks to reduce portfolio volatility through its investments in Underlying ETFs that invest primarily in domestic investment-grade fixed income securities. Target allocations are reviewed by SSGA FM at least monthly and may be adjusted as the market and economic outlook changes. Generally, any changes among asset classes will be within a range of plus or minus 5 percentage points per asset class per quarter; however, SSGA FM may at times make larger allocation changes if it believes market conditions warrant a larger change, and at any time the target allocation to a certain asset class may be zero. SSGA FM reserves the right to replace Underlying ETFs or other securities in its asset allocation model at any time, although such changes would generally be the result of a change in the target allocation with respect to an asset class. Although the Portfolio currently invests primarily in Underlying ETFs, it may also invest in other types of securities, including open-end investment companies, such as high yield bond funds, and cash equivalents, such as money market funds or repurchase agreements. In addition, SSGA FM may choose to achieve a target allocation to cash by entering into repurchase agreements, directly purchasing money market instruments, or purchasing Underlying ETFs that invest in cash securities. For additional information about the Portfolio’s investment strategies and where to find more detailed information about the Portfolio’s investments in the Underlying ETFs, please see “Additional Information about the Portfolio’s Investment Strategies” in the Prospectus.

State Street Moderately Aggressive ETF Portfolio Investment Strategy - State Street Moderately Aggressive ETF Portfolio

Dec. 31, 2025

<span style="color:#000000;font-family:Times New Roman;font-size:11.5pt;font-weight:bold;">Principal Investment Strategies</span>

Strategy Narrative [Text Block]

SSGA Funds Management, Inc. (“SSGA FM” or “Subadviser”), subadviser to the Portfolio, invests, under normal circumstances, at least 80% of the Portfolio’s net assets in investment companies known as exchange-traded funds (the “Underlying ETFs”), including exchange-traded funds advised by SSGA FM. The Portfolio allocates its assets among various asset classes. SSGA FM establishes specific investment percentages for the asset classes and then selects the Underlying ETFs in which the Portfolio invests. The Portfolio invests a significant portion of its assets in Underlying ETFs that invest primarily in the U.S. and international equity markets with moderate allocations to Underlying ETFs that invest primarily in fixed income securities in an effort to reduce portfolio volatility in difficult market environments. In an effort to achieve its investment objectives and reduce portfolio volatility over an intermediate-term cycle, equity investments are allocated across a range of asset classes, which can include, but are not limited to, varying market capitalization categories (large, mid and small), U.S. and foreign real estate investment trust (“REIT”), and foreign developed and emerging markets, and the Portfolio’s fixed income investments may be allocated across a range of sectors which can include, but are not limited to, government, inflation protected government (both U.S. Treasury Inflation Protected Securities (“TIPS”) and equivalent foreign securities), bank loans, and U.S. and foreign debt securities, including emerging market debt securities, as well as investment grade corporate debt securities and lower rated, higher-yielding debt securities (commonly referred to as “junk bonds”). In addition, the Portfolio may invest in other asset classes (e.g., commodities) through exchange traded investment vehicles. The following chart describes the strategic target allocations, as of April 27, 2026, among the range of equities, fixed income and cash/money market securities for the Portfolio. You should note that these target allocations may not directly correspond to investment in the Underlying ETFs because each Underlying ETF may contain various subsets of an asset class (e.g., large cap and mid cap equity securities), and the target allocations are subject to review and modification by SSGA FM. In addition to investing in Underlying ETFs, the Portfolio may invest in other exchange traded vehicles such as exchange traded notes and exchange traded grantor trusts.Asset ClassTarget Allocation*Equities80%U.S. Large Cap35%U.S. Mid Cap4.5%U.S. Small Cap4.5%International Equity18.5%International Small Cap3%Emerging Market Equity9.5%Real Estate Investment Trusts1%International Real Estate Investment Trusts1%Commodities3%Fixed Income18%U.S. Fixed Income13.5%High Yield1.5%Bank Loans1.5%Emerging Market Debt1.5%Treasury Inflation-Protected Securities0%Cash/Cash Equivalents2%*Individual figures may not add up to the totals shown due to rounding. Although the Portfolio will invest new assets and reinvest dividends based on the target allocations at such time, the Portfolio’s target allocations could change substantially over time as the Underlying ETFs’ asset values change due to market movements and portfolio management decisions. The Portfolio currently seeks to achieve capital growth through its investments in Underlying ETFs that invest primarily in equity securities of large U.S. and foreign companies. The Portfolio currently seeks to reduce portfolio volatility through its investments in Underlying ETFs that invest primarily in domestic investment-grade fixed income securities. Target allocations are reviewed by SSGA FM at least monthly and may be adjusted as the market and economic outlook changes. Generally, any changes among asset classes will be within a range of plus or minus 5 percentage points per asset class per quarter; however, SSGA FM may at times make larger allocation changes if it believes market conditions warrant a larger change, and at any time the target allocation to a certain asset class may be zero. SSGA FM reserves the right to replace Underlying ETFs or other securities in its asset allocation model at any time, although such changes would generally be the result of a change in the target allocation with respect to an asset class. Although the Portfolio currently invests primarily in Underlying ETFs, it may also invest in other types of securities, including open-end investment companies, such as high yield bond funds, and cash equivalents, such as money market funds or repurchase agreements. In addition, SSGA FM may choose to achieve a target allocation to cash by entering into repurchase agreements, directly purchasing money market instruments, or purchasing Underlying ETFs that invest in cash securities. For additional information about the Portfolio’s investment strategies and where to find more detailed information about the Portfolio’s investments in the Underlying ETFs, please see “Additional Information about the Portfolio’s Investment Strategies” in the Prospectus.