v3.25.2
Shareholder Report, Holdings (Details)
Apr. 30, 2025
Fidelity Treasury Money Market Fund - Advisor Class C | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 67.60%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.00%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.30%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Treasury Money Market Fund - Advisor Class C | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Treasury Money Market Fund - Advisor Class C | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 67.60%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.00%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.30%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Treasury Money Market Fund - Daily Money Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Treasury Money Market Fund - Daily Money Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Tax-Exempt Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 78.60%
Fidelity Tax-Exempt Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Tax-Exempt Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.50%
Fidelity Tax-Exempt Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Fidelity Tax-Exempt Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Tax-Exempt Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Tax-Exempt Money Market Fund | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 40.80%
Fidelity Tax-Exempt Money Market Fund | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 27.60%
Fidelity Tax-Exempt Money Market Fund | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.40%
Fidelity Tax-Exempt Money Market Fund | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Tax-Exempt Money Market Fund | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 11.10%
Fidelity Treasury Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 67.60%
Fidelity Treasury Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.00%
Fidelity Treasury Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Treasury Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.30%
Fidelity Treasury Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Treasury Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Treasury Money Market Fund | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Treasury Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 78.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.50%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 40.80%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 27.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.40%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 11.10%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 78.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.50%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 40.80%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 27.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.40%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 11.10%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 67.60%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 17.00%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.30%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Treasury Money Market Fund - Capital Reserves Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Treasury Money Market Fund - Capital Reserves Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 50.70%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 78.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.50%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 40.80%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 27.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.40%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 11.10%