S000014681 [Member] Annual Total Returns |
12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Western Asset SMASh Series M Fund | SMASh Series M Fund | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | (1.71%) | 5.15% | (23.27%) | (3.66%) | 12.87% | 7.71% | 1.45% | 6.25% | 4.47% | 3.73% |