State Street Institutional Treasury Money Market Fund Performance Management - State Street Institutional Treasury Money Market Fund |
Dec. 31, 2025 |
|---|---|
| Prospectus [Line Items] | |
| Bar Chart and Performance Table [Heading] | <span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">Performance</span> |
| Performance Narrative [Text Block] | The bar chart and table below provide some indication of the risks of investing in the Treasury Fund by illustrating the variability of the Fund's returns from year-to-year. The historical returns of Premier Class shares, which are not offered in this prospectus, are shown since Mercury Class shares are new. Returns of the Mercury Class shares would have been similar to the returns shown for Premier Class because each share class is invested in the same portfolio of securities. Returns would differ only to the extent that the new share class does not have the same expenses as Premier Class shares. Mercury Class shares are generally expected to incur higher expenses, and have lower returns, than Premier Class shares. 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.statestreet.com/im. |
| Performance Past Does Not Indicate Future [Text] | <span style="color:#000000;font-family:Arial;font-size:10.02pt;">The Fund's past performance </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">does not necessarily indicate how the Fund will perform in the future.</span> |
| Performance Information Illustrates Variability of Returns [Text] | <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 Treasury Fund by illustrating the variability of the Fund's returns from year-to-year. </span> |
| Bar Chart, Returns for Class Not Offered in Prospectus [Text] | <span style="color:#000000;font-family:Arial;font-size:10.02pt;">The </span><span style="color:#000000;font-family:Arial;font-size:10.02pt;margin-left:0%;">historical returns of Premier Class shares, which are not offered in this prospectus, are shown since Mercury Class shares are new. Returns of the Mercury Class shares would have been similar to the returns shown for Premier Class because each share class is invested in the same portfolio of securities.</span> |
| Bar Chart [Heading] | <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] | ReturnsQuarter/YearHighest Quarterly Return1.34%Q4 2023Lowest Quarterly Return0.00%Q3 2021 |
| Performance Table Heading | <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 12/31/25)</span> |
| Performance Table Narrative | To obtain the Fund's current yield, please call (877) 521-4083. |
| Money Market Seven Day Yield Phone | <span style="color:#000000;font-family:Arial;font-size:10.02pt;">(877) 521-4083</span> |
| Performance Availability Website Address [Text] | <span style="color:#000000;font-family:Arial;font-size:10.02pt;">www.statestreet.com/im</span> |
| Performance Availability Phone [Text] | <span style="color:#000000;font-family:Arial;font-size:10.02pt;">(877) 521-4083</span> |
| Premier Class | |
| Prospectus [Line Items] | |
| Highest Quarterly Return, Label [Optional Text] | <span style="color:#000000;font-family:Arial;font-size:9.02pt;font-weight:bold;margin-left:0.0pt;">Highest Quarterly Return</span> |
| Highest Quarterly Return | 1.34% |
| Highest Quarterly Return, Date | Dec. 31, 2023 |
| Lowest Quarterly Return, Label [Optional Text] | <span style="color:#000000;font-family:Arial;font-size:9.02pt;font-weight:bold;margin-left:0.0pt;">Lowest Quarterly Return</span> |
| Lowest Quarterly Return | none |
| Lowest Quarterly Return, Date | Sep. 30, 2021 |