Risk/Return Detail Data - FidelityTreasuryDigitalFund-OnChainPRO |
Sep. 22, 2025 |
|---|---|
| FidelityTreasuryDigitalFund-OnChainPRO | | |
| Prospectus Line Items | |
| Supplement to Prospectus [Text Block] | Supplement to theFidelity® Treasury Digital FundOnChainJuly 25, 2025Prospectus |
| Strategy Narrative [Text Block] | Normally investing at least 99.5% of total assets in cash and U.S. Treasury securities. The fund intends to invest only in cash and U.S. Treasury securities with a remaining maturity of 93 days or less or issued with a maturity of 93 days or less. |
| FidelityTreasuryDigitalFund-LiquidityPRO | | |
| Prospectus Line Items | |
| Supplement to Prospectus [Text Block] | Supplement to theFidelity® Treasury Digital FundLiquidityJune 28, 2025Prospectus |
| Strategy Narrative [Text Block] | Normally investing at least 99.5% of total assets in cash and U.S. Treasury securities. The fund intends to invest only in cash and U.S. Treasury securities with a remaining maturity of 93 days or less or issued with a maturity of 93 days or less. |
| Document Type | 497 |
| Registrant Name | Fidelity Hereford Street Trust |