Risk/Return Detail Data - FidelityFixed-IncomeActiveETFs-ComboPRO |
Sep. 18, 2026 |
|---|---|
| FidelityFixed-IncomeActiveETFs-ComboPRO | | |
| Prospectus Line Items | |
| Supplement to Prospectus [Text Block] | Supplement to theFidelity® Corporate Bond ETF, Fidelity® Investment Grade Bond ETF, Fidelity® Investment Grade Securitized ETF, Fidelity® Limited Term Bond ETF, and Fidelity® Total Bond ETFDecember 30, 2025Prospectus |
| Strategy Narrative [Text Block] | Investing up to 30% of assets in lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds). The following information supplements information for Fidelity® Limited Term Bond ETF found in the "Fund Summary" section under the "Principal Investment Strategies" heading. Investing in collateralized loan obligations (CLO). |
| Document Type | 497 |
| Registrant Name | Fidelity Merrimack Street Trust |