| Form N-CSR Cover | 6 Months Ended |
| Sep. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Legg Mason ETF Investment Trust |
| Entity Central Index Key | 0001645194 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Sep. 30, 2024 |
| Shareholder Report | 6 Months Ended | |
| Sep. 30, 2024 USD ($) $ / shares | ||
| Shareholder Report [Line Items] | ||
| Document Type | N-CSRS | |
| Amendment Flag | false | |
| Registrant Name | Legg Mason ETF Investment Trust | |
| Entity Central Index Key | 0001645194 | |
| Entity Investment Company Type | N-1A | |
| Document Period End Date | Sep. 30, 2024 | |
| Royce Quant Small-Cap Quality Value ETF | ||
| Shareholder Report [Line Items] | ||
| Fund Name | Royce Quant Small-Cap Quality Value ETF | |
| Class Name | Royce Quant Small-Cap Quality Value ETF | |
| Trading Symbol | SQLV | |
| Security Exchange Name | NASDAQ | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about Royce Quant Small-Cap Quality Value ETF for the period April 1, 2024, to September 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 1-877-721-1926 or 1-203-703-6002 . | |
| Additional Information Phone Number | 1-877-721-1926 or 1-203-703-6002 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment) Fund Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment † Royce Quant Small-Cap Quality Value ETF $30 0.60% | [1] |
| Expenses Paid, Amount | $ 30 | |
| Expense Ratio, Percent | 0.60% | |
| Net Assets | $ 29,423,950 | |
| Holdings Count | $ / shares | 271 | [2] |
| Investment Company Portfolio Turnover | 19% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of September 30, 2024) Total Net Assets $29,423,950 Total Number of Portfolio Holdings * 271 Portfolio Turnover Rate 19% | [2] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| [1] † Annualized. * Does not include derivatives, except purchased options, if any. | ||
| Label | Element | Value |
| Royce Quant Small-Cap Quality Value ETF | Health Care [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 18.60% |
| Royce Quant Small-Cap Quality Value ETF | Financials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 18.60% |
| Royce Quant Small-Cap Quality Value ETF | Industrials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 15% |
| Royce Quant Small-Cap Quality Value ETF | Information Technology [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 12.70% |
| Royce Quant Small-Cap Quality Value ETF | Consumer Discretionary [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 11.90% |
| Royce Quant Small-Cap Quality Value ETF | Energy [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 7.50% |
| Royce Quant Small-Cap Quality Value ETF | Consumer Staples [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 4.70% |
| Royce Quant Small-Cap Quality Value ETF | Materials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 4.50% |
| Royce Quant Small-Cap Quality Value ETF | Communication Services [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 4.30% |
| Royce Quant Small-Cap Quality Value ETF | Real Estate [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 1.10% |
| Royce Quant Small-Cap Quality Value ETF | Utilities [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 1% |
| Royce Quant Small-Cap Quality Value ETF | Short-Term Investments [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 0.10% |
