Shareholder Report
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6 Months Ended |
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Jun. 30, 2026
USD ($)
Holding
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| Shareholder Report [Line Items] |
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| Document Type |
N-CSRS
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| Amendment Flag |
false
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| Registrant Name |
STATE STREET MASTER FUNDS
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| Entity Central Index Key |
0001094885
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| Entity Investment Company Type |
N-1A
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| Document Period End Date |
Jun. 30, 2026
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| Shareholder Report Annual or Semi-Annual |
Semi-Annual Shareholder Report
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| C000170903 |
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| Shareholder Report [Line Items] |
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| Fund Name |
State Street International Developed Equity Index Portfolio
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| No Trading Symbol [Flag] |
true
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| Annual or Semi-Annual Statement [Text Block] |
This semi-annual shareholder report contains important information about the State Street International Developed Equity Index Portfolio (the "Fund") for the period of January 1, 2026 through June 30, 2026.
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| Additional Information [Text Block] |
You can request additional information about the Fund by contacting us at 1-800-647-7327.
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| Additional Information Phone Number |
1-800-647-7327
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| Expenses [Text Block] |
What were the Fund costs for the last six months? (based on a hypothetical $10,000 Investment)
Table Summary
Fund Name |
Costs of a $10,000 investment |
Costs paid as a percentage of a $10,000 investment |
State Street International Developed Equity Index Portfolio |
$7 |
0.14%Footnote Reference* |
| Footnote |
Description |
Footnote* |
Annualized. | |
|
| Expenses Paid, Amount |
$ 7
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|
| Expense Ratio, Percent |
0.14%
|
[1] |
| AssetsNet |
$ 4,449,212,616
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| Holdings Count | Holding |
679
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| InvestmentCompanyPortfolioTurnover |
5.00%
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| Additional Fund Statistics [Text Block] |
Key Fund Statistics as of 6/30/2026- Total Net Assets$4,449,212,616
- Number of Portfolio Holdings679
- Portfolio Turnover Rate5%
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| Holdings [Text Block] |
Table Summary
Countries |
% |
Japan |
22.9% |
United Kingdom |
10.8% |
Germany |
8.5% |
France |
8.0% |
United States |
7.2% |
Australia |
7.0% |
Switzerland |
6.2% |
Netherlands |
5.9% |
Spain |
3.7% |
Italy |
3.2% | |
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| Largest Holdings [Text Block] |
Table Summary
Holdings |
% |
ASML Holding NV |
3.5% |
HSBC Holdings PLC |
1.5% |
Roche Holding AG |
1.3% |
Novartis AG |
1.3% |
AstraZeneca PLC |
1.3% |
Nestle SA |
1.2% |
Siemens AG |
1.1% |
Shell PLC |
1.0% |
Tokyo Electron Ltd. |
1.0% |
Mitsubishi UFJ Financial Group, Inc. |
1.0% | |
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| C000055942 |
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| Shareholder Report [Line Items] |
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| Fund Name |
State Street Treasury Money Market Portfolio
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| No Trading Symbol [Flag] |
true
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| Annual or Semi-Annual Statement [Text Block] |
This semi-annual shareholder report contains important information about the State Street Treasury Money Market Portfolio (the "Fund") for the period of January 1, 2026 through June 30, 2026.
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| Additional Information [Text Block] |
You can request additional information about the Fund by contacting us at 1-866-392-0869.
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| Additional Information Phone Number |
1-866-392-0869
|
|
| Expenses [Text Block] |
What were the Fund costs for the last six months? (based on a hypothetical $10,000 Investment)
Table Summary
Fund Name |
Costs of a $10,000 investment |
Costs paid as a percentage of a $10,000 investment |
State Street Treasury Money Market Portfolio |
$3 |
0.06%Footnote Reference* |
| Footnote |
Description |
Footnote* |
Annualized. | |
|
| Expenses Paid, Amount |
$ 3
|
|
| Expense Ratio, Percent |
0.06%
|
[2] |
| AssetsNet |
$ 15,697,287,916
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| Holdings Count | Holding |
62
|
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| Additional Fund Statistics [Text Block] |
Key Fund Statistics as of 6/30/2026- Total Net Assets$15,697,287,916
- Number of Portfolio Holdings62
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| Holdings [Text Block] |
Table Summary
Asset |
% |
Treasury Debt |
103.8% | |
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| Largest Holdings [Text Block] |
Table Summary
Holdings |
% |
U.S. Treasury Bills, 3.58%, due 07/02/26 |
13.8% |
U.S. Treasury Bills, 3.48%, due 07/09/26 |
8.6% |
U.S. Treasury Bills, 3.61%, due 07/14/26 |
7.8% |
U.S. Treasury Bills, 3.62%, due 07/07/26 |
5.8% |
U.S. Treasury Floating Rate Notes, 3.96%, due 07/31/26 |
4.2% |
U.S. Treasury Bills, 3.63%, due 08/18/26 |
3.8% |
U.S. Treasury Bills, 3.64%, due 09/17/26 |
3.6% |
U.S. Treasury Bills, 3.50%, due 08/13/26 |
3.6% |
U.S. Treasury Bills, 3.61%, due 07/28/26 |
3.2% |
U.S. Treasury Bills, 3.66%, due 08/25/26 |
3.2% | |
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| C000055943 |
|
|
| Shareholder Report [Line Items] |
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| Fund Name |
State Street Treasury Plus Money Market Portfolio
|
|
| No Trading Symbol [Flag] |
true
|
|
| Annual or Semi-Annual Statement [Text Block] |
This semi-annual shareholder report contains important information about the State Street Treasury Plus Money Market Portfolio (the "Fund") for the period of January 1, 2026 through June 30, 2026.
|
|
| Additional Information [Text Block] |
You can request additional information about the Fund by contacting us at 1-866-392-0869.
|
|
| Additional Information Phone Number |
1-866-392-0869
|
|
| Expenses [Text Block] |
What were the Fund costs for the last six months? (based on a hypothetical $10,000 Investment)
Table Summary
Fund Name |
Costs of a $10,000 investment |
Costs paid as a percentage of a $10,000 investment |
State Street Treasury Plus Money Market Portfolio |
$3 |
0.06%Footnote Reference* |
| Footnote |
Description |
Footnote* |
Annualized. | |
|
| Expenses Paid, Amount |
$ 3
|
|
| Expense Ratio, Percent |
0.06%
|
[3] |
| AssetsNet |
$ 85,676,695,642
|
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| Holdings Count | Holding |
96
|
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| Additional Fund Statistics [Text Block] |
Key Fund Statistics as of 6/30/2026- Total Net Assets$85,676,695,642
- Number of Portfolio Holdings96
|
|
| Holdings [Text Block] |
Table Summary
Assets |
% |
Treasury Repurchase Agreements |
57.9% |
Treasury Debt |
35.0% | |
|
| Largest Holdings [Text Block] |
Table Summary
Holdings |
% |
JP Morgan Sec LLC Tpr A, 3.64%, due 07/01/26 |
11.2% |
FICCRP Tri Party Repo A, 3.64%, due 07/01/26 |
7.0% |
FICCIN Tri Party Repo A, 3.64%, due 07/01/26 |
3.5% |
BBVARP BBVARP Tri Party Repo A, 3.64%, due 07/01/26 |
3.0% |
FICCBA Tri Party Repo A, 3.65%, due 07/01/26 |
2.9% |
FICCWB Tri Party Repo A, 3.64%, due 07/01/26 |
2.8% |
FICCNT Bi Party Repo, 3.64%, due 07/01/26 |
2.6% |
U.S. Treasury Floating Rate Notes, 3.88%, due 01/31/28 |
2.6% |
Goldman Sachs Tri Party A, 3.64%, due 07/01/26 |
2.5% |
CIBC NY CORP Tri Party Repo A, 3.64%, due 07/01/26 |
2.3% | |
|
| C000029566 |
|
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| Shareholder Report [Line Items] |
|
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| Fund Name |
State Street U.S. Government Money Market Portfolio
|
|
| No Trading Symbol [Flag] |
true
|
|
| Annual or Semi-Annual Statement [Text Block] |
This semi-annual shareholder report contains important information about the State Street U.S. Government Money Market Portfolio (the "Fund") for the period of January 1, 2026 through June 30, 2026.
|
|
| Additional Information [Text Block] |
You can request additional information about the Fund by contacting us at 1-866-392-0869.
|
|
| Additional Information Phone Number |
1-866-392-0869
|
|
| Expenses [Text Block] |
What were the Fund costs for the last six months? (based on a hypothetical $10,000 Investment)
Table Summary
Fund Name |
Costs of a $10,000 investment |
Costs paid as a percentage of a $10,000 investment |
State Street U.S. Government Money Market Portfolio |
$3 |
0.06%Footnote Reference* |
| Footnote |
Description |
Footnote* |
Annualized. | |
|
| Expenses Paid, Amount |
$ 3
|
|
| Expense Ratio, Percent |
0.06%
|
[4] |
| AssetsNet |
$ 229,945,214,292
|
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| Holdings Count | Holding |
241
|
|
| Additional Fund Statistics [Text Block] |
Key Fund Statistics as of 6/30/2026- Total Net Assets$229,945,214,292
- Number of Portfolio Holdings241
|
|
| Holdings [Text Block] |
Table Summary
Assets |
% |
Treasury Repurchase Agreements |
32.8% |
Treasury Debt |
28.3% |
Government Agency Repurchase Agreements |
18.0% |
Government Agency Debt |
12.5% | |
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| Largest Holdings [Text Block] |
Table Summary
Holdings |
% |
JP Morgan Sec LLC Tpr A, 3.64%, due 07/01/26 |
5.1% |
FICCMS Tri Party Repo D, 3.65%, due 07/01/26 |
3.9% |
FICCMS Tri Party Repo A, 3.64%, due 07/01/26 |
3.5% |
FICCBA Tri Party Repo A, 3.65%, due 07/01/26 |
3.5% |
Goldman Sacs Tri Party D, 3.65%, due 07/01/26 |
3.0% |
FICCUB Bi Party Repo, 3.66%, due 07/01/26 |
2.6% |
FICCIN Tri Party Repo A, 3.64%, due 07/01/26 |
2.6% |
FICCWB Tri Party Repo A, 3.64%, due 07/01/26 |
2.5% |
FICCNT Bi Party Repo, 3.64%, due 07/01/26 |
2.4% |
FICCNT Bi Party Repo, 3.65%, due 07/01/26 |
1.7% | |
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