State Street Small Cap Equity VIS Fund Investment Strategy - State Street Small Cap Equity VIS Fund	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	The Fund seeks to achieve its investment objective by investing at least 80% of its net assets (plus any borrowings for investment purposes) under normal circumstances in equity securities of small-cap companies, such as common and preferred stocks. The Fund defines a small-cap company as one with a market capitalization that, at the time of initial investment, falls between (a) the market capitalization of the smallest company in the Russell 2000® Index and (b) either the larger of the market capitalization of the largest company in the Russell 2000® Index or $3.0 billion. As of February 28, 2026, the market capitalizations of companies in the Russell 2000® Index ranged from $6.34 million to $39.26 billion. These capitalization ranges will change over time. SSGA Funds Management, Inc. (“SSGA FM” or the “Adviser”), the Fund's investment adviser, or a sub-adviser will not sell a stock merely because the market capitalization of a company in the portfolio moves outside of this capitalization range or because the index capitalization range changes. Because of this, the Fund may have less than 80% of its net assets in equity securities of small-cap companies at any given time. The Adviser and sub-advisers select equity securities from a number of industries based on the merits of individual companies, although at times the Fund's investments may be focused in one or more market sectors, such as information technology.The Fund uses a multi sub-adviser investment strategy that combines growth, value and core investment management styles. SSGA FM will allocate the Fund's assets among the sub-advisers to maintain exposure to a combination of investment styles, but may have larger allocations to certain sub-advisers based on its assessment of the potential for better performance or to address capacity constraints of a particular sub-adviser, among other reasons. As a result, this orientation will typically produce a portfolio that does not materially favor value or growth style investing, and allows the Fund the potential to benefit from both value and growth cycles in the marketplace. The Adviser and sub-advisers seek to identify securities of companies that they believe have desirable characteristics for the Fund such as: •high quality management focused on generating shareholder value; •attractive products or services; •appropriate capital structures; and/or •strong competitive positions in their industries. In addition, a sub-adviser with a value investment style generally will seek to identify securities of companies with characteristics such as attractive valuation, while a sub-adviser with a growth investment style generally will seek to identify securities of companies with strong growth potential. The Adviser and sub-advisers may consider selling a security when one of these characteristics no longer applies, when the Adviser or sub-adviser believes that the valuation has become excessive, or more attractive alternatives are identified.The Fund also may invest up to 20% of its net assets (plus any borrowings for investment purposes) in securities with capitalizations outside the Fund's small-cap range and up to 10% of its total assets in foreign securities. The Fund also may invest up to 20% of its net assets (plus any borrowings for investment purposes) in debt securities and up to 10% in below-investment grade debt securities. The Adviser and sub-advisers may also use various types of derivative instruments (such as futures contracts, options and forward contracts) to gain or hedge exposure to certain types of securities as an alternative to investing directly in or selling such securities.

State Street Small Cap Equity VIS Fund Investment Strategy - State Street Small Cap Equity VIS Fund

Dec. 31, 2025

<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Investment Strategies</span>

Strategy Narrative [Text Block]

The Fund seeks to achieve its investment objective by investing at least 80% of its net assets (plus any borrowings for investment purposes) under normal circumstances in equity securities of small-cap companies, such as common and preferred stocks. The Fund defines a small-cap company as one with a market capitalization that, at the time of initial investment, falls between (a) the market capitalization of the smallest company in the Russell 2000® Index and (b) either the larger of the market capitalization of the largest company in the Russell 2000® Index or $3.0 billion. As of February 28, 2026, the market capitalizations of companies in the Russell 2000® Index ranged from $6.34 million to $39.26 billion. These capitalization ranges will change over time. SSGA Funds Management, Inc. (“SSGA FM” or the “Adviser”), the Fund's investment adviser, or a sub-adviser will not sell a stock merely because the market capitalization of a company in the portfolio moves outside of this capitalization range or because the index capitalization range changes. Because of this, the Fund may have less than 80% of its net assets in equity securities of small-cap companies at any given time. The Adviser and sub-advisers select equity securities from a number of industries based on the merits of individual companies, although at times the Fund's investments may be focused in one or more market sectors, such as information technology.The Fund uses a multi sub-adviser investment strategy that combines growth, value and core investment management styles. SSGA FM will allocate the Fund's assets among the sub-advisers to maintain exposure to a combination of investment styles, but may have larger allocations to certain sub-advisers based on its assessment of the potential for better performance or to address capacity constraints of a particular sub-adviser, among other reasons. As a result, this orientation will typically produce a portfolio that does not materially favor value or growth style investing, and allows the Fund the potential to benefit from both value and growth cycles in the marketplace. The Adviser and sub-advisers seek to identify securities of companies that they believe have desirable characteristics for the Fund such as: •high quality management focused on generating shareholder value; •attractive products or services; •appropriate capital structures; and/or •strong competitive positions in their industries. In addition, a sub-adviser with a value investment style generally will seek to identify securities of companies with characteristics such as attractive valuation, while a sub-adviser with a growth investment style generally will seek to identify securities of companies with strong growth potential. The Adviser and sub-advisers may consider selling a security when one of these characteristics no longer applies, when the Adviser or sub-adviser believes that the valuation has become excessive, or more attractive alternatives are identified.The Fund also may invest up to 20% of its net assets (plus any borrowings for investment purposes) in securities with capitalizations outside the Fund's small-cap range and up to 10% of its total assets in foreign securities. The Fund also may invest up to 20% of its net assets (plus any borrowings for investment purposes) in debt securities and up to 10% in below-investment grade debt securities. The Adviser and sub-advisers may also use various types of derivative instruments (such as futures contracts, options and forward contracts) to gain or hedge exposure to certain types of securities as an alternative to investing directly in or selling such securities.