S000069099 [Member] Performance Management - WESTERN ASSET SMASh SERIES CORE COMPLETION FUND |
Feb. 28, 2025 |
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| Prospectus [Line Items] | |
| Bar Chart and Performance Table [Heading] | Performance |
| Performance Narrative [Text Block] | The accompanying bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year. The table shows the average annual total returns of the fund and also compares the fund’s performance with the average annual total returns of a broad measure of market performance. Updated performance information for the fund may be obtained by calling the fund at 877-6LM-FUND/656-3863. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. Sales charges are not reflected in the accompanying bar chart, and if those charges were included, returns would be less than those shown. Sales charges do not apply to purchases of fund shares by managed account program participants, but (as discussed above), managed account program participants pay fees to program sponsors for the costs and expenses of such programs. In addition, performance does not reflect the fees and expenses paid by participants in separately managed account programs to program sponsors. You should evaluate the performance of the fund in the context of your managed account program.
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| Performance Past Does Not Indicate Future [Text] | The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. |
| Performance Information Illustrates Variability of Returns [Text] | The bar chart shows changes in the fund’s performance from year to year. The table shows the average annual total returns of the fund and also compares the fund’s performance with the average annual total returns of a broad measure of market performance. |
| Bar Chart Does Not Reflect Sales Loads [Text] | Sales charges are not reflected in the accompanying bar chart, and if those charges were included, returns would be less than those shown. |
| Bar Chart [Heading] | Total returns (%) Before taxes |
| Bar Chart Closing [Text Block] | Calendar Years ended December 31 Best Quarter (12/31/2023): 5.75 Worst Quarter (03/31/2022): (14.35) The year-to-date return as of the most recent calendar quarter, which ended March 31, 2025, was 1.16 |
| Performance Table Heading | Average annual total returns (%)(for periods ended December 31, 2024) |
| Performance Table Narrative | The after-tax returns shown are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. Returns after taxes on distributions and sale of fund shares are higher than returns before taxes for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of fund shares.
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| Performance Table Uses Highest Federal Rate | The after-tax returns shown are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. |
| Performance Table Explanation after Tax Higher | Returns after taxes on distributions and sale of fund shares are higher than returns before taxes for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of fund shares. |
| Performance Availability Phone [Text] | 877-6LM-FUND/656-3863 |
| SMASh SERIES CORE COMPLETION FUND | |
| Prospectus [Line Items] | |
| Year to Date Return, Label [Optional Text] | year-to-date return |
| Bar Chart, Year to Date Return | 1.16% |
| Bar Chart, Year to Date Return, Date | Mar. 31, 2025 |
| Highest Quarterly Return, Label [Optional Text] | Best Quarter |
| Highest Quarterly Return | 5.75% |
| Highest Quarterly Return, Date | Dec. 31, 2023 |
| Lowest Quarterly Return, Label [Optional Text] | Worst Quarter |
| Lowest Quarterly Return | (14.35%) |
| Lowest Quarterly Return, Date | Mar. 31, 2022 |