State Street Income VIS Fund Investment Strategy - State Street Income 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 debt securities. The Fund invests primarily in a variety of investment-grade debt securities, such as mortgage-backed securities, corporate bonds, U.S. Government securities and money market instruments. The Fund normally has a weighted average effective maturity of approximately five to ten years, but is subject to no limitation with respect to the maturities of the instruments in which it may invest. U.S. Government securities are securities that are issued or guaranteed as to principal or interest by the U.S. Government or one of its agencies or instrumentalities. Some U.S. Government securities are backed by the full faith and credit of the U.S. Government, such as U.S. Treasury bills and notes and obligations of the Government National Mortgage Association (“Ginnie Mae”). Other U.S. Government securities are neither issued by nor guaranteed by the full faith and credit of the U.S. Government, including those issued by the Federal National Mortgage Association (“Fannie Mae”) and the Federal Home Loan Mortgage Corporation (“Freddie Mac”). Fannie Mae and Freddie Mac have been operating under a conservatorship since 2008, with the Federal Housing Finance Agency acting as their conservator, and receive certain financing support from and have access to certain borrowing arrangements with the U.S. Treasury. The Fund's investment adviser, SSGA Funds Management, Inc. (the “Adviser” or “SSGA FM”) seeks to identify debt securities that they believe have desirable characteristics for the Fund such as: •attractive yields and prices; •the potential for capital appreciation; and/or •reasonable credit quality. The Adviser may consider selling a security when one of these characteristics no longer applies, when the Adviser believes that the valuation has become excessive, or when more attractive alternatives are identified. The Fund also may invest up to 45% of its net assets in securities rated BBB or below by S&P Global Ratings (“S&P”) or Baa or below by Moody's Investor Services, Inc. (“Moody's”) or of similar quality and up to 20% of its net assets in high yield securities (also known as below investment grade bonds or “junk bonds”). The Fund may also invest in exchange-traded products (“ETPs”) that provide exposure to such investments, including ETPs that pay fees to the Adviser and its affiliates for management, marketing or other services. High yield securities are those rated BB+ through B- by S&P or Ba1 through B3 by Moody's or below or of similar quality. The Fund also may invest up to 35% of its total assets in foreign (including emerging markets) debt securities, and up to 20% of its net assets (plus any borrowings for investment purposes) in equity securities. The Fund may also invest in municipal obligations and asset-backed securities. The Adviser may also use various types of derivative instruments (such as futures contracts, interest rate and credit default swaps, options and forward contracts) to manage yield, duration (a measure of a bond price's sensitivity to a given change in interest rates) and exposure to credit quality, and to gain or hedge exposure to certain securities, indices or market segments.The Fund may engage in active and frequent trading of its portfolio securities.

State Street Income VIS Fund Investment Strategy - State Street Income 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 debt securities. The Fund invests primarily in a variety of investment-grade debt securities, such as mortgage-backed securities, corporate bonds, U.S. Government securities and money market instruments. The Fund normally has a weighted average effective maturity of approximately five to ten years, but is subject to no limitation with respect to the maturities of the instruments in which it may invest. U.S. Government securities are securities that are issued or guaranteed as to principal or interest by the U.S. Government or one of its agencies or instrumentalities. Some U.S. Government securities are backed by the full faith and credit of the U.S. Government, such as U.S. Treasury bills and notes and obligations of the Government National Mortgage Association (“Ginnie Mae”). Other U.S. Government securities are neither issued by nor guaranteed by the full faith and credit of the U.S. Government, including those issued by the Federal National Mortgage Association (“Fannie Mae”) and the Federal Home Loan Mortgage Corporation (“Freddie Mac”). Fannie Mae and Freddie Mac have been operating under a conservatorship since 2008, with the Federal Housing Finance Agency acting as their conservator, and receive certain financing support from and have access to certain borrowing arrangements with the U.S. Treasury. The Fund's investment adviser, SSGA Funds Management, Inc. (the “Adviser” or “SSGA FM”) seeks to identify debt securities that they believe have desirable characteristics for the Fund such as: •attractive yields and prices; •the potential for capital appreciation; and/or •reasonable credit quality. The Adviser may consider selling a security when one of these characteristics no longer applies, when the Adviser believes that the valuation has become excessive, or when more attractive alternatives are identified. The Fund also may invest up to 45% of its net assets in securities rated BBB or below by S&P Global Ratings (“S&P”) or Baa or below by Moody's Investor Services, Inc. (“Moody's”) or of similar quality and up to 20% of its net assets in high yield securities (also known as below investment grade bonds or “junk bonds”). The Fund may also invest in exchange-traded products (“ETPs”) that provide exposure to such investments, including ETPs that pay fees to the Adviser and its affiliates for management, marketing or other services. High yield securities are those rated BB+ through B- by S&P or Ba1 through B3 by Moody's or below or of similar quality. The Fund also may invest up to 35% of its total assets in foreign (including emerging markets) debt securities, and up to 20% of its net assets (plus any borrowings for investment purposes) in equity securities. The Fund may also invest in municipal obligations and asset-backed securities. The Adviser may also use various types of derivative instruments (such as futures contracts, interest rate and credit default swaps, options and forward contracts) to manage yield, duration (a measure of a bond price's sensitivity to a given change in interest rates) and exposure to credit quality, and to gain or hedge exposure to certain securities, indices or market segments.The Fund may engage in active and frequent trading of its portfolio securities.