v3.26.1
Shareholder Report, Holdings (Details)
Apr. 30, 2026
Fidelity Treasury Only Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 19.90%
Fidelity Treasury Only Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.90%
Fidelity Treasury Only Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 24.10%
Fidelity Treasury Only Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 21.00%
Fidelity Treasury Only Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 16.40%
Fidelity Treasury Only Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Fidelity Treasury Only Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 100.90%
Fidelity Series Treasury Bill Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 99.20%
Fidelity Series Treasury Bill Index Fund | CD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 99.20%
Fidelity Series Treasury Bill Index Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.20%
Fidelity Series Treasury Bill Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 53.80%
Fidelity Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.10%
Fidelity Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 15.00%
Fidelity Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.90%
Fidelity Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 32.60%
Fidelity Money Market Fund | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.90%
Fidelity Money Market Fund | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.40%
Fidelity Money Market Fund | AATimeDepositsMember  
Holdings [Line Items]  
Percent of Net Asset Value 5.60%
Fidelity Money Market Fund | AACertificatesofDepositMember  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Money Market Fund - Premium Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 53.80%
Fidelity Money Market Fund - Premium Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Money Market Fund - Premium Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.10%
Fidelity Money Market Fund - Premium Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 15.00%
Fidelity Money Market Fund - Premium Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.90%
Fidelity Money Market Fund - Premium Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Money Market Fund - Premium Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 32.60%
Fidelity Money Market Fund - Premium Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.90%
Fidelity Money Market Fund - Premium Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.40%
Fidelity Money Market Fund - Premium Class | AATimeDepositsMember  
Holdings [Line Items]  
Percent of Net Asset Value 5.60%
Fidelity Money Market Fund - Premium Class | AACertificatesofDepositMember  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Government Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Premium Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Premium Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Premium Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Premium Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Premium Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Premium Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Premium Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Premium Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Premium Class | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Daily Money Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Daily Money Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Daily Money Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Daily Money Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Daily Money Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Daily Money Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Daily Money Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Daily Money Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Daily Money Class | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Class S | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Class S | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Class S | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Class S | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Class S | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Class S | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Class S | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Class S | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Class S | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Class K6 | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Class K6 | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Class K6 | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Class K6 | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Class K6 | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Class K6 | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Class K6 | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Class K6 | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Class K6 | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Capital Reserves Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Capital Reserves Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Capital Reserves Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Capital Reserves Class | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Government Money Market Fund - Class M | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 62.90%
Fidelity Government Money Market Fund - Class M | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Government Money Market Fund - Class M | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Government Money Market Fund - Class M | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity Government Money Market Fund - Class M | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity Government Money Market Fund - Class M | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Government Money Market Fund - Class M | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 28.60%
Fidelity Government Money Market Fund - Class M | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 41.00%
Fidelity Government Money Market Fund - Class M | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 31.60%
Fidelity Flex Government Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 59.40%
Fidelity Flex Government Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.20%
Fidelity Flex Government Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.50%
Fidelity Flex Government Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Flex Government Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 15.20%
Fidelity Flex Government Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Flex Government Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 27.40%
Fidelity Flex Government Money Market Fund | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 38.30%
Fidelity Flex Government Money Market Fund | AAUSGovernmentAgencyDebtMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.80%
Fidelity Flex Government Money Market Fund | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Treasury Digital Fund - Liquidity | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.50%
Fidelity Treasury Digital Fund - Liquidity | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 24.20%
Fidelity Treasury Digital Fund - Liquidity | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 38.50%
Fidelity Treasury Digital Fund - Liquidity | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 31.50%
Fidelity Treasury Digital Fund - Liquidity | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 104.70%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 19.90%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.90%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 24.10%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 21.00%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 16.40%
Fidelity Treasury Only Money Market Fund - Class OUS | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Fidelity Treasury Only Money Market Fund - Class OUS | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 100.90%
Fidelity Treasury Digital Fund - OnChain Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.50%
Fidelity Treasury Digital Fund - OnChain Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 24.20%
Fidelity Treasury Digital Fund - OnChain Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 38.50%
Fidelity Treasury Digital Fund - OnChain Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 31.50%
Fidelity Treasury Digital Fund - OnChain Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 104.70%