Label |
Element |
Value |
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Registrant Name |
dei_EntityRegistrantName |
STATE STREET INSTITUTIONAL INVESTMENT TRUST
|
|
Prospectus Date |
rr_ProspectusDate |
Apr. 30, 2025
|
|
State Street Treasury Obligations Money Market Fund |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk/Return [Heading] |
rr_RiskReturnHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;text-transform:uppercase;">State Street Treasury Obligations Money Market Fund</span>
|
|
Objective [Heading] |
rr_ObjectiveHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Investment Objective</span>
|
|
Objective, Primary [Text Block] |
rr_ObjectivePrimaryTextBlock |
The investment objective of State Street Treasury Obligations Money Market Fund (the “Treasury Obligations Fund” or sometimes referred to in context as the “Fund”) is to seek a high level of current income consistent with preserving principal and liquidity and the maintenance of a stable $1.00 per share net asset value (“NAV”).
|
|
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>
|
|
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 Treasury Obligations 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 Treasury Plus Money Market Portfolio (the “Treasury Plus Portfolio” or sometimes referred to in context as the “Portfolio”).
|
|
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>
|
|
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>
|
|
Expense Example [Heading] |
rr_ExpenseExampleHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Example:</span>
|
|
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 periods takes into account the effect of the current contractual fee waivers and/or reimbursements. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
|
|
Strategy [Heading] |
rr_StrategyHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Investment Strategies</span>
|
|
Strategy Narrative [Text Block] |
rr_StrategyNarrativeTextBlock |
The Fund is a government money market fund and attempts to meet its investment objective by investing only in U.S. Treasury bills, notes and bonds (which are direct obligations of the U.S. government) and repurchase agreements collateralized by these obligations. The Fund may hold a portion of its assets in cash pending investment, to satisfy redemption requests or to meet the Fund's other cash management needs. The Fund invests in accordance with regulatory requirements applicable to money market funds, which require, among other things, the Fund to invest only in short-term securities (generally, securities that have remaining maturities of 397 calendar days or less, with the exception of certain floating rate securities that may have final maturities longer than 397 days but use maturity shortening provisions to meet the 397 day requirement, and that the Fund believes present minimal credit risk), to maintain a maximum dollar-weighted average maturity and dollar-weighted average life of sixty (60) days or less and 120 days or less, respectively, and to meet requirements as to portfolio diversification and liquidity. The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the Treasury Plus Portfolio, which has substantially identical investment policies to the Fund. When the Fund invests in this “master-feeder” structure, the Fund's only investments are shares of the Treasury Plus Portfolio, and it participates in the investment returns achieved by the Treasury Plus Portfolio. Descriptions in this section of the investment activities of the “Fund” also generally describe the expected investment activities of the Treasury Plus Portfolio.
|
|
Risk [Heading] |
rr_RiskHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Principal Risks</span>
|
|
Bar Chart and Performance Table [Heading] |
rr_BarChartAndPerformanceTableHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Performance</span>
|
|
Performance Narrative [Text Block] |
rr_PerformanceNarrativeTextBlock |
The bar chart and table below provide some indication of the risks of investing in the Treasury Obligations Fund by illustrating the variability of the Fund's returns from year-to-year.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 (877) 521-4083 or by visiting our website at www.ssga.com.
|
|
Performance Information Illustrates Variability of Returns [Text] |
rr_PerformanceInformationIllustratesVariabilityOfReturns |
<span style="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 Treasury Obligations Fund by illustrating the variability of the Fund's returns from year-to-year.</span>
|
|
Performance Availability Phone [Text] |
rr_PerformanceAvailabilityPhone |
<span style="font-family:Arial;font-size:10.02pt;">(877) 521-4083</span>
|
|
Performance Availability Website Address [Text] |
rr_PerformanceAvailabilityWebSiteAddress |
<span style="font-family:Arial;font-size:10.02pt;"> www.ssga.com</span>
|
|
Performance Past Does Not Indicate Future [Text] |
rr_PerformancePastDoesNotIndicateFuture |
<span style="font-family:Arial;font-size:10.02pt;">The Fund's past performance does not necessarily</span><span style="font-family:Arial;font-size:10.02pt;margin-left:0%;"> indicate how the Fund will perform in the future.</span>
|
|
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>
|
|
Bar Chart Closing [Text Block] |
rr_BarChartClosingTextBlock |
ReturnsQuarter/YearHighest Quarterly Return1.35%Q4 2023Lowest Quarterly Return0.01%Q3 2021
|
|
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>
|
|
Performance Table Narrative |
rr_PerformanceTableNarrativeTextBlock |
To obtain the Fund's current yield, please call (877) 521-4083.
|
|
Money Market Seven Day Yield Phone |
rr_MoneyMarketSevenDayYieldPhone |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;">(877) 521-4083</span>
|
|
State Street Treasury Obligations Money Market Fund | Risk Lose Money [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
You could lose money by investing in the Fund.
|
|
State Street Treasury Obligations Money Market Fund | Risk Money Market Fund May Not Preserve Dollar [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so.
|
|
State Street Treasury Obligations Money Market Fund | Risk Money Market Fund Sponsor May Not Provide Support [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
The Fund's sponsor is not required to reimburse the Fund for losses, and you should not expect that the sponsor will provide financial support to the Fund at any time, including during periods of market stress.
|
|
State Street Treasury Obligations Money Market Fund | Risk Not Insured Depository Institution [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
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.
|
|
State Street Treasury Obligations Money Market Fund | Money Market Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Money Market Fund Risk: An investment in a money market fund is not a deposit of any bank and is not insured or guaranteed by the FDIC or any other government agency. Although a money market fund generally seeks to preserve the value of its shares at $1.00 per share, there can be no assurance that it will do so, and it is possible to lose money by investing in a money market fund. A major or unexpected change in interest rates or a decline in the credit quality of an issuer or entity providing credit support, an inactive trading market for money market instruments, or adverse market, economic, industry, political, regulatory, geopolitical, and other conditions could cause a money market fund's share price to fall below $1.00.
|
|
State Street Treasury Obligations Money Market Fund | US Treasury Obligations Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
U.S. Treasury Obligations Risk: U.S. Treasury obligations may differ from other fixed income securities in their interest rates, maturities, times of issuance and other characteristics. Similar to other issuers, changes to the financial condition or credit rating of the U.S. government may cause the value of the Fund's U.S. Treasury obligations to decline.
|
|
State Street Treasury Obligations Money Market Fund | Repurchase Agreement Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Repurchase Agreement Risk: Repurchase agreements may be viewed as loans made by the Fund, which are collateralized by the securities subject to repurchase. If the Fund's counterparty should default on its obligations and the Fund is delayed or prevented from recovering the collateral, or if the value of the collateral is insufficient, the Fund may realize a loss.
|
|
State Street Treasury Obligations Money Market Fund | Stable Share Price Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Stable Share Price Risk: If the market value of one or more of the Fund's investments changes substantially, the Fund may not be able to maintain a stable share price of $1.00. This risk typically is higher during periods of rapidly changing interest rates or when issuer credit quality generally is falling, and is made worse when the Fund experiences significant redemption requests.
|
|
State Street Treasury Obligations Money Market Fund | Market Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
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.
|
|
State Street Treasury Obligations Money Market Fund | Low Short Term Interest Rate Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Low Short-Term Interest Rates: During market conditions in which short-term interest rates are at low levels, the Fund's yield can be very low. During these conditions, it is possible that the Fund will generate an insufficient amount of income to pay its expenses, and that it will not be able to pay a daily dividend and may have a negative yield (i.e., it may lose money on an operating basis). It is possible that the Fund would, during these conditions, maintain a substantial portion of its assets in cash, on which it may earn little, if any, income.
|
|
State Street Treasury Obligations Money Market Fund | Counterparty Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
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 repurchase agreements and other transactions. If a counterparty fails to meet its contractual obligations, the Fund may be unable to terminate the transaction, and it may be delayed or prevented from realizing on any collateral in the event of a bankruptcy or insolvency proceeding relating to the counterparty.
|
|
State Street Treasury Obligations Money Market Fund | Debt Securities Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Debt Securities Risk: The values of debt securities may increase or decrease as a result of the following: market fluctuations, changes in interest rates, actual or perceived inability or unwillingness of issuers, guarantors or liquidity providers to make scheduled principal or interest payments, or illiquidity in debt securities markets. To the extent that interest rates rise, certain underlying obligations may be paid off substantially slower than originally anticipated and the value of those securities may fall sharply. A rising interest rate environment may cause the value of the Fund's fixed income securities to decrease, an adverse impact on the liquidity of the Fund's fixed income securities, and increased volatility of the fixed income markets. During periods when interest rates are at low levels, the Fund's yield can be low, and the Fund may have a negative yield (i.e., it may lose money on an operating basis). To the extent that interest rates fall, certain underlying obligations may be paid off substantially faster than originally anticipated. If the principal on a debt obligation is prepaid before expected, the prepayments of principal may have to be reinvested in obligations paying interest at lower rates. During periods of falling interest rates, the income received by the Fund may decline. Changes in interest rates will likely have a greater effect on the values of debt securities of longer durations. Returns on investments in debt securities could trail the returns on other investment options, including investments in equity securities. High levels of inflation and/or a significantly changing interest rate environment can lead to heightened levels of volatility and reduced liquidity.
|
|
State Street Treasury Obligations Money Market Fund | Interest Rate Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Interest Rate Risk: Interest rate risk is the risk that debt securities will decline in value because of increases in interest rates. The value of a security with a longer duration will be more sensitive to changes in interest rates than a similar security with a shorter duration. Interest-only and principal-only securities are especially sensitive to interest rate changes, which can affect not only their prices but can also change the income flows and repayment assumptions about those investments.
|
|
State Street Treasury Obligations Money Market Fund | Large Transactions Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Large Transactions Risk: To the extent a large proportion of the interests of the Portfolio or Fund are held by a small number of investors (or a single investor), including funds or accounts over which the Adviser has investment discretion, the Fund is subject to the risk that these investors will purchase or redeem Portfolio or Fund interests 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 Portfolio or 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.
|
|
State Street Treasury Obligations Money Market Fund | Master Feeder Structure Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
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.
|
|
State Street Treasury Obligations Money Market Fund | Rapid Changes in Interest Rates Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Rapid Changes in Interest Rates Risk: Rapid changes in interest rates may cause significant requests to redeem Fund Shares, and possibly cause the Fund to sell portfolio securities at a loss to satisfy those requests.
|
|
State Street Treasury Obligations Money Market Fund | Variable and Floating Rate Securities Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Variable and Floating Rate Securities Risk: During periods of increasing interest rates, changes in the coupon rates of variable or floating rate securities may lag behind the changes in market rates or may have limits on the maximum increases in coupon rates. Alternatively, during periods of declining interest rates, the coupon rates on such securities will typically readjust downward resulting in a lower yield.
|
|
State Street Treasury Obligations Money Market Fund | Focused Investment Risk [Member] |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Risk [Text Block] |
rr_RiskTextBlock |
Focused Investment Risk: To the extent the Fund invests a large percentage of its assets in securities within the same country, state, region, or economic sector its investment strategy could result in more risk or greater volatility in returns than if the Fund's investments were less focused.
|
|
State Street Treasury Obligations Money Market Fund | State Street Treasury Obligations Money Market Fund |
|
|
|
Risk Return Abstract |
rr_RiskReturnAbstract |
|
|
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) |
rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice |
none
|
|
Maximum Deferred Sales Charge (Load) (as a percentage of the lower of the sale proceeds or the original offering price) |
rr_MaximumDeferredSalesChargeOverOther |
none
|
|
Management Fee |
rr_ManagementFeesOverAssets |
0.05%
|
|
Distribution and/or Shareholder Service (12b-1) Fees |
rr_DistributionAndService12b1FeesOverAssets |
none
|
|
Other Expenses |
rr_OtherExpensesOverAssets |
0.07%
|
|
Total Annual Fund Operating Expenses |
rr_ExpensesOverAssets |
0.12%
|
|
Less Fee Waivers and/or Expense Reimbursements |
rr_FeeWaiverOrReimbursementOverAssets |
(0.02%)
|
[1] |
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements |
rr_NetExpensesOverAssets |
0.10%
|
[1] |
1 year |
rr_ExpenseExampleYear01 |
$ 10
|
|
3 years |
rr_ExpenseExampleYear03 |
37
|
|
5 years |
rr_ExpenseExampleYear05 |
66
|
|
10 years |
rr_ExpenseExampleYear10 |
$ 152
|
|
2018 |
rr_AnnualReturn2018 |
1.79%
|
|
2019 |
rr_AnnualReturn2019 |
2.16%
|
|
2020 |
rr_AnnualReturn2020 |
0.44%
|
|
2021 |
rr_AnnualReturn2021 |
0.02%
|
|
2022 |
rr_AnnualReturn2022 |
1.64%
|
|
2023 |
rr_AnnualReturn2023 |
5.10%
|
|
2024 |
rr_AnnualReturn2024 |
5.26%
|
|
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>
|
|
Highest Quarterly Return, Date |
rr_BarChartHighestQuarterlyReturnDate |
Dec. 31, 2023
|
|
Highest Quarterly Return |
rr_BarChartHighestQuarterlyReturn |
1.35%
|
|
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>
|
|
Lowest Quarterly Return, Date |
rr_BarChartLowestQuarterlyReturnDate |
Sep. 30, 2021
|
|
Lowest Quarterly Return |
rr_BarChartLowestQuarterlyReturn |
0.01%
|
|
OneYear |
rr_AverageAnnualReturnYear01 |
5.26%
|
|
FiveYears |
rr_AverageAnnualReturnYear05 |
2.47%
|
|
Since Inception |
rr_AverageAnnualReturnSinceInception |
2.28%
|
|
Inception Date |
rr_AverageAnnualReturnInceptionDate |
Oct. 05, 2017
|
|
|
|