v3.26.1
Shareholder Report, Holdings (Details)
Apr. 30, 2026
Fidelity Treasury Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 65.60%
Fidelity Treasury Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.00%
Fidelity Treasury Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Treasury Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.70%
Fidelity Treasury Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Treasury Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Treasury Money Market Fund | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 56.10%
Fidelity Treasury Money Market Fund | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 45.80%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 65.60%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.00%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.70%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Treasury Money Market Fund - Daily Money Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Treasury Money Market Fund - Daily Money Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 56.10%
Fidelity Treasury Money Market Fund - Daily Money Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 45.80%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 65.60%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.00%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.70%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Treasury Money Market Fund - Capital Reserves Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Treasury Money Market Fund - Capital Reserves Class | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 56.10%
Fidelity Treasury Money Market Fund - Capital Reserves Class | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 45.80%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 65.60%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.00%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.70%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Treasury Money Market Fund - Advisor Class C | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Treasury Money Market Fund - Advisor Class C | AAUSTreasuryObligationsMember  
Holdings [Line Items]  
Percent of Net Asset Value 56.10%
Fidelity Treasury Money Market Fund - Advisor Class C | AARepurchaseAgreementsMember  
Holdings [Line Items]  
Percent of Net Asset Value 45.80%
Fidelity Tax-Exempt Money Market Fund | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 73.80%
Fidelity Tax-Exempt Money Market Fund | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Tax-Exempt Money Market Fund | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity Tax-Exempt Money Market Fund | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.50%
Fidelity Tax-Exempt Money Market Fund | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.60%
Fidelity Tax-Exempt Money Market Fund | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.50%
Fidelity Tax-Exempt Money Market Fund | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.60%
Fidelity Tax-Exempt Money Market Fund | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Tax-Exempt Money Market Fund | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 73.80%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity Tax-Exempt Money Market Fund - Premium Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.50%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.50%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.60%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Tax-Exempt Money Market Fund - Premium Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 73.80%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.50%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.50%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.60%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Tax-Exempt Money Market Fund - Daily Money Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD0Member  
Holdings [Line Items]  
Percent of Net Asset Value 73.80%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD1Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD2Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD3Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD4Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | EMD5Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.50%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AATenderOptionBondMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AAVariableRateDemandNotesVRDNsMember  
Holdings [Line Items]  
Percent of Net Asset Value 33.50%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AAMunicipalSecuritiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.60%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AACommercialPaperMember  
Holdings [Line Items]  
Percent of Net Asset Value 10.70%
Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | AANetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%