Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	Other
Document Period End Date	dei_DocumentPeriodEndDate	Aug. 31, 2011
Registrant Name	dei_EntityRegistrantName	Vanguard Money Market Reserves
Central Index Key	dei_EntityCentralIndexKey	0000106830
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Sep. 11, 2012
Document Effective Date	dei_DocumentEffectiveDate	Aug. 31, 2012
Vanguard Federal Money Market Fund | Participant
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Dec. 27, 2011
Operating Expenses Caption	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Vanguard Federal Money Market Fund | Retail
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Dec. 27, 2011
Operating Expenses Caption	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Vanguard Federal Money Market Fund | Vanguard Federal Money Market Fund - Investor Shares
Risk/Return:	rr_RiskReturnAbstract
Management Expenses	rr_ManagementFeesOverAssets	0.16%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.04%
Total Annual Fund Operating Expenses	rr_NetExpensesOverAssets	0.20%	[1]
1 YEAR	rr_ExpenseExampleNoRedemptionYear01	20
3 YEAR	rr_ExpenseExampleNoRedemptionYear03	64
5 YEAR	rr_ExpenseExampleNoRedemptionYear05	113
10 YEAR	rr_ExpenseExampleNoRedemptionYear10	255

[1] Vanguard and the Fund's Board have voluntarily agreed to temporarily limit certain net operating expenses in excess of the Fund's daily yield so as to maintain a zero or positive yield for the Fund. Vanguard and the Fund's Board may terminate the temporary expense limitation at any time.