Label |
Element |
Value |
Risk Return Abstract |
rr_RiskReturnAbstract |
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Registrant Name |
dei_EntityRegistrantName |
STATE STREET INSTITUTIONAL INVESTMENT TRUST
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Prospectus Date |
rr_ProspectusDate |
Apr. 30, 2025
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Administrative Shares | State Street Equity 500 Index Fund |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk/Return [Heading] |
rr_RiskReturnHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;text-transform:uppercase;">State Street Equity 500 Index Fund</span>
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Objective [Heading] |
rr_ObjectiveHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Investment Objective</span>
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Objective, Primary [Text Block] |
rr_ObjectivePrimaryTextBlock |
The investment objective of the State Street Equity 500 Index Fund (the “Equity 500 Index Fund” or sometimes referred to in context as the “Fund”) is to replicate as closely as possible, before expenses, the performance of the Standard & Poor's 500 Index (the “S&P 500” or sometimes referred to in context as the “Index”).
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Expense [Heading] |
rr_ExpenseHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Fees and Expenses of the Fund</span>
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Expense Narrative [Text Block] |
rr_ExpenseNarrativeTextBlock |
The tables below describe the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund (“Fund Shares”). You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. The expenses shown in the table and the Example reflect the expenses of the Fund and the Fund's proportionate share of the expenses of the State Street Equity 500 Index II Portfolio (the “Equity 500 Index II Portfolio” or sometimes referred to in context as the “Portfolio”).
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Shareholder Fees Caption [Text] |
rr_ShareholderFeesCaption |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Shareholder Fees </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;">(fees paid directly from your investment)</span>
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Operating Expenses Caption [Text] |
rr_OperatingExpensesCaption |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Annual Fund Operating Expenses </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;">(expenses that you pay each year as a percentage of the value of your investment)</span>
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Fee Waiver or Reimbursement over Assets, Date of Termination |
rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination |
<span style="font-family:Arial;font-size:9.02pt;">April 30, 2026</span>
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Portfolio Turnover [Heading] |
rr_PortfolioTurnoverHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Portfolio Turnover:</span>
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Portfolio Turnover [Text Block] |
rr_PortfolioTurnoverTextBlock |
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). As a shareholder of the Portfolio, the Fund bears its ratable share of the transaction costs associated with the portfolio turnover of the Portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund Shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 4% of the average value of its portfolio.
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Portfolio Turnover, Rate |
rr_PortfolioTurnoverRate |
4.00%
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Expenses Restated to Reflect Current [Text] |
rr_ExpensesRestatedToReflectCurrent |
<span style="color:#000000;font-family:Arial;font-size:9.02pt;">Other Expenses have been restated to reflect current fees.</span>
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Expense Example [Heading] |
rr_ExpenseExampleHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Example:</span>
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Expense Example Narrative [Text Block] |
rr_ExpenseExampleNarrativeTextBlock |
This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell or hold all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The calculation of costs for the one-year period takes into account the effect of any current contractual fee waivers and/or reimbursements; and the calculation of costs for the remaining periods takes such fee waivers and/or reimbursements into account only for the first year of each such period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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Strategy [Heading] |
rr_StrategyHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Investment Strategies</span>
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Strategy Narrative [Text Block] |
rr_StrategyNarrativeTextBlock |
The Fund uses a passive management strategy designed to track the performance of the S&P 500. The Index is a well-known stock market index that includes common stocks of 500 companies from a number of sectors and that measures the performance of the large-cap sector of the U.S. equities market. As of February 28, 2025, a significant portion of the Index comprised companies in the information technology, healthcare and financials sectors, although this may change from time to time. The Fund is not managed according to traditional methods of “active” investment management, which involve the buying and selling of securities based upon economic, financial and market analysis and investment judgment. Instead, the Fund, using a “passive” or “indexing” investment approach, seeks to provide investment results that, before expenses, correspond generally to the total return of the S&P 500. The Fund generally intends to invest in all stocks comprising the S&P 500 in approximate proportion to their weightings in the Index. However, under various circumstances, it may not be possible or practicable to purchase all stocks in those weightings. In those circumstances, the Fund may purchase a sample of the stocks in the Index in proportions expected by SSGA Funds Management, Inc. (“SSGA FM” or the “Adviser”), the investment adviser to the Fund, to match generally the performance of the Index as a whole. In addition, from time to time, stocks are added to or removed from the Index. The Fund may sell securities that are represented in the Index, or purchase securities that are not yet represented in the Index, in anticipation of their removal from or addition to the Index. Under normal market conditions, the Fund will not invest less than 80% of its total assets in stocks in the Index. Shareholders will receive sixty (60) days' notice prior to a change in the 80% investment policy. For this purpose, “total assets” means net assets plus borrowings, if any. The notional value of the Fund's investments in derivatives or other synthetic instruments that provide exposures comparable, in the judgment of the Adviser, to investments in the Index may be counted toward satisfaction of this 80% policy. In addition, the Fund may invest in equity securities that are not included in the Index, cash and cash equivalents or money market instruments, such as repurchase agreements and money market funds (including money market funds advised by the Adviser). The Fund may at times purchase or sell futures contracts, or options on those futures, in lieu of investing directly in the stocks making up the Index. The Fund might do so, for example, in order to increase its investment exposure pending investment of cash in the stocks comprising the Index. Alternatively, the Fund might use futures or options on futures to reduce its investment exposure in situations where it intends to sell a portion of the stocks in its portfolio but the sale has not yet been completed. The Fund may also enter into other derivatives transactions, including the use of options or swap transactions, in lieu of investing directly in the stocks making up the Index. The Fund may also, to the extent permitted by applicable law, invest in shares of other mutual funds whose investment objectives and policies are similar to those of the Fund (including funds advised by the Adviser). The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the Equity 500 Index II Portfolio, which has substantially similar investment policies to the Fund. When the Fund invests in this “master-feeder” structure, the Fund's only investments are shares of the Portfolio, and it participates in the investment returns achieved by the Portfolio. Descriptions in this section of the investment activities of the “Fund” also generally describe the expected investment activities of the Portfolio.
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Risk [Heading] |
rr_RiskHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Risks</span>
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Bar Chart and Performance Table [Heading] |
rr_BarChartAndPerformanceTableHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Performance</span>
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Performance Narrative [Text Block] |
rr_PerformanceNarrativeTextBlock |
The bar chart and table below provide some indication of the risks of investing in the Fund by illustrating the variability of the Fund's' returns from year-to-year and by showing how the Fund's average annual returns for the periods indicated compared with those of the Index. The bar chart shows how the Administrative Shares' returns have varied for each full calendar year shown. The Fund's past performance does not necessarily indicate how the Fund will perform in the future. Current performance information for the Fund is available toll free by calling (800) 997-7327 or by visiting our website at www.ssga.com.
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Performance Information Illustrates Variability of Returns [Text] |
rr_PerformanceInformationIllustratesVariabilityOfReturns |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">The bar chart and table below provide some indication of the risks of investing in the Fund by illustrating the variability of the Fund's' returns from year-to-year and by showing how the Fund's average annual returns for the periods indicated compared with those of the Index.</span>
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Performance Availability Phone [Text] |
rr_PerformanceAvailabilityPhone |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;">(800) 997-7327</span>
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Performance Availability Website Address [Text] |
rr_PerformanceAvailabilityWebSiteAddress |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;">www.ssga.com</span>
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Performance Past Does Not Indicate Future [Text] |
rr_PerformancePastDoesNotIndicateFuture |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;">The Fund's past performance does </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">not necessarily indicate how the Fund will perform in the future.</span>
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Bar Chart [Heading] |
rr_BarChartHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Annual Total Returns </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;">(years ended 12/31)</span>
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Bar Chart Closing [Text Block] |
rr_BarChartClosingTextBlock |
ReturnsQuarter/YearHighest Quarterly Return20.45%Q2 2020Lowest Quarterly Return-19.60%Q1 2020
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Performance Table Heading |
rr_PerformanceTableHeading |
<span style="font-family:Arial;font-size:10.02pt;font-weight:bold;">Average Annual Total Returns </span><span style="font-family:Arial;font-size:10.02pt;">(for periods ended 12/31/24)</span>
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Performance Table Uses Highest Federal Rate |
rr_PerformanceTableUsesHighestFederalRate |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. </span>
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Performance Table Not Relevant to Tax Deferred |
rr_PerformanceTableNotRelevantToTaxDeferred |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;">After-tax returns depend on an investor's tax situation and may differ from those </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">shown, and after-tax returns are not relevant to investors who hold their shares through tax-advantaged arrangements, </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;">such as 401(k) plans or individual retirement accounts (“IRAs”).</span>
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Performance Table Narrative |
rr_PerformanceTableNarrativeTextBlock |
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. After-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”).
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Performance Table Closing [Text Block] |
rr_PerformanceTableClosingTextBlock |
The Fund will make updated performance information, including its current net asset value, available at the Fund's website:www.ssga.com.
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Administrative Shares | State Street Equity 500 Index Fund | Risk Lose Money [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
You could lose money by investing in the Fund.
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Administrative Shares | State Street Equity 500 Index Fund | Risk Not Insured Depository Institution [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
An investment in the Fund is subject to investment risks, including possible loss of principal, is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.
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Administrative Shares | State Street Equity 500 Index Fund | Market Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Market Risk: The Fund's investments are subject to changes in general economic conditions, general market fluctuations and the risks inherent in investment in securities markets. Investment markets can be volatile and prices of investments can change substantially due to various factors including, but not limited to, economic growth or recession, changes in interest rates, inflation, changes in the actual or perceived creditworthiness of issuers, and general market liquidity. The Fund is subject to the risk that geopolitical events will disrupt securities markets and adversely affect global economies and markets. Local, regional or global events such as war, military conflicts, acts of terrorism,trade policy changes or disputes, the threat or actual imposition of tariffs, natural disasters, the spread of infectious illness or other public health issues, or other events could have a significant impact on the Fund and its investments.
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Administrative Shares | State Street Equity 500 Index Fund | Equity Investing Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Equity Investing Risk: The market prices of equity securities owned by the Fund may go up or down, sometimes rapidly or unpredictably. The value of a security may decline for a number of reasons that may directly relate to the issuer and also may decline due to general industry or market conditions that are not specifically related to a particular company. In addition, equity markets tend to move in cycles, which may cause stock prices to fall over short or extended periods of time.
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Administrative Shares | State Street Equity 500 Index Fund | Information Technology Sector Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Information Technology Sector Risk: Market or economic factors impacting information technology companies could have a major effect on the value of the Fund's investments. The value of stocks of information technology companies is particularly vulnerable to rapid changes in technology product cycles, rapid product obsolescence, government regulation and competition, both domestically and internationally, including competition from foreign competitors with lower production costs. Like other technology companies, information technology companies may have limited product lines, markets, financial resources or personnel. Stocks of technology companies and companies that rely heavily on technology, especially those of smaller, less-seasoned companies, tend to be more volatile than the overall market. Information technology companies are heavily dependent on patent and intellectual property rights, the loss or impairment of which may adversely affect profitability. Additionally, companies in the information technology sector may face dramatic and often unpredictable changes in growth rates and competition for the services of qualified personnel.
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Administrative Shares | State Street Equity 500 Index Fund | Indexing Strategy Index Tracking Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Indexing Strategy/Index Tracking Risk: The Fund is managed with an indexing investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the Index or of the actual securities comprising the Index. This differs from an actively-managed fund, which typically seeks to outperform a benchmark index. As a result, the Fund's performance may be less favorable than that of a portfolio managed using an active investment strategy. The structure and composition of the Index will affect the performance, volatility, and risk of the Index and, consequently, the performance, volatility, and risk of the Fund. While the Adviser seeks to track the performance of the Index (i.e., achieve a high degree of correlation with the Index), the Fund's return may not match the return of the Index. The Fund incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. In addition, the Fund may not be fully invested at times, generally as a result of cash flows into or out of the Fund or reserves of cash held by the Fund to meet redemptions. The Adviser may attempt to replicate the Index return by investing in fewer than all of the securities in the Index, or in some securities not included in the Index, potentially increasing the risk of divergence between the Fund's return and that of the Index.
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Administrative Shares | State Street Equity 500 Index Fund | Counterparty Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Counterparty Risk: The Fund will be subject to credit risk with respect to the counterparties with which the Fund enters into derivatives contracts, repurchase agreements, reverse repurchase agreements, and other transactions. If a counterparty fails to meet its contractual obligations, the Fund may be unable to terminate or realize any gain on the investment or transaction, or to recover collateral posted to the counterparty, resulting in a loss to the Fund. If the Fund holds collateral posted by its counterparty, it may be delayed or prevented from realizing on the collateral in the event of a bankruptcy or insolvency proceeding relating to the counterparty.
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Administrative Shares | State Street Equity 500 Index Fund | Derivatives Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Derivatives Risk: Derivative transactions can create investment leverage and may have significant volatility. It is possible that a derivative transaction will result in a much greater loss than the principal amount invested, that changes in the value of a derivative transaction may not correlate perfectly with the underlying asset, and that the Fund may not be able to close out a derivative transaction at a favorable time or price. The counterparty to a derivatives contract may be unable or unwilling to make timely settlement payments, return the Fund's margin, or otherwise honor its obligations. A derivatives transaction may not behave in the manner anticipated by the Adviser or may not have the effect on the Fund anticipated by the Adviser.
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Administrative Shares | State Street Equity 500 Index Fund | Financial Sector Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Financial Sector Risk: Financial services companies are subject to extensive governmental regulation, which may limit both the amounts and types of loans and other financial commitments they can make, the interest rates and fees they can charge, the scope of their activities, the prices they can charge and the amount of capital they must maintain. Profitability is largely dependent on the availability and cost of capital funds and can fluctuate significantly when interest rates change or due to increased competition. In addition, deterioration of the credit markets generally may cause an adverse impact in a broad range of markets, including U.S. and international credit and interbank money markets generally, thereby affecting a wide range of financial institutions and markets. Certain events in the financial sector may cause an unusually high degree of volatility in the financial markets, both domestic and foreign, and cause certain financial services companies to incur large losses. Securities of financial services companies may experience a dramatic decline in value when such companies experience substantial declines in the valuations of their assets, take action to raise capital (such as the issuance of debt or equity securities), or cease operations. Credit losses resulting from financial difficulties of borrowers and financial losses associated with investment activities can negatively impact the sector. Insurance companies may be subject to severe price competition. Adverse economic, business or political developments could adversely affect financial institutions engaged in mortgage finance or other lending or investing activities directly or indirectly connected to the value of real estate.
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Administrative Shares | State Street Equity 500 Index Fund | Health Care Sector Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Healthcare Sector Risk: Companies in the healthcare sector are subject to extensive government regulation and their profitability can be significantly affected by restrictions on government reimbursement for medical expenses, rising costs of medical products and services, pricing pressure (including price discounting), limited product lines and an increased emphasis on the delivery of healthcare through outpatient services. Companies in the healthcare sector are heavily dependent on obtaining and defending patents, which may be time consuming and costly, and the expiration of patents may also adversely affect the profitability of these companies. Healthcare companies are also subject to extensive litigation based on product liability and similar claims. In addition, their products can become obsolete due to industry innovation, changes in technologies or other market developments. Many new products in the healthcare sector require significant research and development and may be subject to regulatory approvals, all of which may be time consuming and costly with no guarantee that any product will come to market.
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Administrative Shares | State Street Equity 500 Index Fund | Large Capitalization Securities Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Large-Capitalization Securities Risk: Returns on investments in securities of large companies could trail the returns on investments in securities of smaller and mid-sized companies. Larger companies may be unable to respond as quickly as smaller and mid-sized companies to competitive challenges or to changes in business, product, financial, or other market conditions. Larger companies may not be able to maintain growth at the high rates that may be achieved by well-managed smaller and mid-sized companies.
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Administrative Shares | State Street Equity 500 Index Fund | Large Transactions Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Large Transactions Risk: To the extent a large proportion of the shares of the Portfolio or Fund are held by a small number of shareholders (or a single shareholder), including funds or accounts over which the Adviser has investment discretion, the Fund is subject to the risk that these shareholders will purchase or redeem Portfolio or Fund shares in large amounts rapidly or unexpectedly, including as a result of an asset allocation decision made by the Adviser. In addition, a large number of shareholders collectively may purchase or redeem Fund shares in large amounts rapidly or unexpectedly (collectively, such transactions are referred to as “large shareholder transactions”). Large shareholder transactions could adversely affect the ability of the Portfolio or Fund to conduct its investment program.
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Administrative Shares | State Street Equity 500 Index Fund | Liquidity Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Liquidity Risk: Lack of a ready market, stressed market conditions, or restrictions on resale may limit the ability of the Fund to sell a security at an advantageous time or price or at all. Illiquid investments may trade at a discount from comparable, more liquid investments and may be subject to wide fluctuations in market value. Illiquidity of the Fund's holdings may also limit the ability of the Fund to obtain cash to meet redemptions on a timely basis. In addition, the Fund, due to limitations on investments in any illiquid investments and/or the difficulty in purchasing and selling such investments, may be unable to achieve its desired level of exposure to a certain market or sector.
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Administrative Shares | State Street Equity 500 Index Fund | Master Feeder Structure Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Master/Feeder Structure Risk: The Fund pursues its objective by investing substantially all of its assets in another pooled investment vehicle (a “master fund”). The ability of the Fund to meet its investment objective is directly related to the ability of the master fund to meet its investment objective. The Adviser serves as investment adviser to the master fund, leading to potential conflicts of interest. The Fund will bear its pro rata portion of the expenses incurred by the master fund. Substantial redemptions by other investors in a master fund may affect the master fund's investment program adversely and limit the ability of the master fund to achieve its objective.
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Administrative Shares | State Street Equity 500 Index Fund | Risk of Investment in Other Pools [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Risk of Investment in Other Pools: If the Fund invests in another pooled investment vehicle, it is exposed to the risk that the other pool will not perform as expected and is exposed indirectly to all of the risks applicable to an investment in such other pool. The investment policies of the other pool may not be the same as those of the Fund; as a result, an investment in the other pool may be subject to additional or different risks than those to which the Fund is typically subject. The Fund bears its proportionate share of the fees and expenses of any pool in which it invests. The Adviser or an affiliate may serve as investment adviser to a pool in which the Fund may invest, leading to potential conflicts of interest. It is possible that other clients of the Adviser or its affiliates will purchase or sell interests in a pool sponsored or managed by the Adviser or its affiliates at prices and at times more favorable than those at which the Fund does so.
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Administrative Shares | State Street Equity 500 Index Fund | Unconstrained Sector Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Unconstrained Sector Risk: The Fund may invest a substantial portion of its assets within one or more economic sectors or industries, which may change from time to time. Greater investment focus on one or more sectors or industries increases the potential for volatility and the risk that events negatively affecting such sectors or industries could reduce returns, potentially causing the value of the Fund's Shares to decrease, perhaps significantly.
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Administrative Shares | State Street Equity 500 Index Fund | Administrative Shares |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) |
rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice |
none
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Maximum Deferred Sales Charge (Load) (as a percentage of the lower of the sale proceeds or the original offering price) |
rr_MaximumDeferredSalesChargeOverOther |
none
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Management Fee |
rr_ManagementFeesOverAssets |
0.02%
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Distribution and/or Shareholder Service (12b-1) Fees |
rr_DistributionAndService12b1FeesOverAssets |
0.15%
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Other Expenses |
rr_OtherExpensesOverAssets |
0.08%
|
[1] |
Total Annual Fund Operating Expenses |
rr_ExpensesOverAssets |
0.25%
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|
Less Fee Waivers and/or Expense Reimbursements |
rr_FeeWaiverOrReimbursementOverAssets |
(0.08%)
|
[2] |
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements |
rr_NetExpensesOverAssets |
0.17%
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|
1 year |
rr_ExpenseExampleYear01 |
$ 17
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|
3 years |
rr_ExpenseExampleYear03 |
72
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5 years |
rr_ExpenseExampleYear05 |
133
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|
10 years |
rr_ExpenseExampleYear10 |
$ 310
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2015 |
rr_AnnualReturn2015 |
1.08%
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|
2016 |
rr_AnnualReturn2016 |
11.75%
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|
2017 |
rr_AnnualReturn2017 |
21.43%
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2018 |
rr_AnnualReturn2018 |
(4.56%)
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2019 |
rr_AnnualReturn2019 |
31.14%
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|
2020 |
rr_AnnualReturn2020 |
18.14%
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|
2021 |
rr_AnnualReturn2021 |
28.32%
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2022 |
rr_AnnualReturn2022 |
(18.28%)
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2023 |
rr_AnnualReturn2023 |
26.08%
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2024 |
rr_AnnualReturn2024 |
24.80%
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Highest Quarterly Return, Label |
rr_HighestQuarterlyReturnLabel |
<span style="font-family:Arial;font-size:9.02pt;font-weight:bold;margin-left:0.0pt;">Highest Quarterly Return</span>
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Highest Quarterly Return, Date |
rr_BarChartHighestQuarterlyReturnDate |
Jun. 30, 2020
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|
Highest Quarterly Return |
rr_BarChartHighestQuarterlyReturn |
20.45%
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|
Lowest Quarterly Return, Label |
rr_LowestQuarterlyReturnLabel |
<span style="font-family:Arial;font-size:9.02pt;font-weight:bold;margin-left:0.0pt;">Lowest Quarterly Return</span>
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|
Lowest Quarterly Return, Date |
rr_BarChartLowestQuarterlyReturnDate |
Mar. 31, 2020
|
|
Lowest Quarterly Return |
rr_BarChartLowestQuarterlyReturn |
(19.60%)
|
|
OneYear |
rr_AverageAnnualReturnYear01 |
24.80%
|
|
FiveYears |
rr_AverageAnnualReturnYear05 |
14.28%
|
|
TenYears |
rr_AverageAnnualReturnYear10 |
12.84%
|
|
Administrative Shares | State Street Equity 500 Index Fund | Return After Taxes on Distributions | Administrative Shares |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
OneYear |
rr_AverageAnnualReturnYear01 |
24.34%
|
|
FiveYears |
rr_AverageAnnualReturnYear05 |
13.76%
|
|
TenYears |
rr_AverageAnnualReturnYear10 |
12.05%
|
|
Administrative Shares | State Street Equity 500 Index Fund | Return After Taxes on Distributions and Sale of Fund Shares | Administrative Shares |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
OneYear |
rr_AverageAnnualReturnYear01 |
14.96%
|
|
FiveYears |
rr_AverageAnnualReturnYear05 |
11.37%
|
|
TenYears |
rr_AverageAnnualReturnYear10 |
10.43%
|
|
Administrative Shares | State Street Equity 500 Index Fund | S&P 500 Index (reflects no deduction for fees, expenses or taxes) |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
OneYear |
rr_AverageAnnualReturnYear01 |
25.02%
|
|
FiveYears |
rr_AverageAnnualReturnYear05 |
14.53%
|
|
TenYears |
rr_AverageAnnualReturnYear10 |
13.10%
|
|
|
|