Risk/Return Detail Data - FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO |
Jul. 11, 2025 |
|---|---|
| FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | | |
| Prospectus Line Items | |
| Supplement to Prospectus [Text Block] | Supplement to theFidelity Flex® FundsFidelity Flex® Mid Cap Index Fund and Fidelity Flex® Small Cap Index FundJune 28, 2025Prospectus |
| Strategy Narrative [Text Block] | Beginning on July 17, 2025, the fund will transition from the Russell Midcap® Index to the Fidelity U.S. Mid Cap IndexSM using a blend of the two indices. The transition will be implemented through six equal stepped transitions effective at the market open on each of the following dates: July 17, 2025, July 24, 2025, July 31, 2025, August 7, 2025, August 14, 2025, and August 21, 2025. The fund's final transition to the Fidelity U.S. Mid Cap IndexSM will be completed at the market close on August 20, 2025. |
| Document Type | 497 |
| Registrant Name | Fidelity Salem Street Trust |