S000052179 [Member] Average Annual Total Returns |
12 Months Ended | 60 Months Ended | 120 Months Ended |
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
|
| Bloomberg Municipal Bond Index (reflects no deduction for fees, expenses or taxes) | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 4.25% | 0.80% | 2.34% |
| Western Asset SMASh Series TF Fund | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 3.37% | 1.32% | 2.72% |
| Western Asset SMASh Series TF Fund | After Taxes on Distributions | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 1.68% | 0.98% | 2.24% |
| Western Asset SMASh Series TF Fund | After Taxes on Distributions and Sales | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 1.96% | 1.44% | 2.31% |