| Label | Element | Value |
|---|---|---|
| Franklin U.S. Treasury Bond ETF | U.S. Government & Agency Obligations [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 95.40% |
| Franklin U.S. Treasury Bond ETF | U.S. Treasury Inflation Protected Securities [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 3.90% |
| Franklin U.S. Treasury Bond ETF | Short-Term Investments [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Total Investments | oef_PctOfTotalInv | 0.70% |