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Annual Fund Operating Expenses (Vanguard Federal Money Market Fund Retail)
Vanguard Federal Money Market Fund
Vanguard Federal Money Market Fund - Investor Shares
9/1/2013 - 8/31/2014
Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)  
Management Fees 0.09%rr_ManagementFeesOverAssets
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= vanguard_C000012238Member
12b-1 Distribution Fee none
Other Expenses 0.02%rr_OtherExpensesOverAssets
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= vanguard_S000004462Member
/ rr_ProspectusShareClassAxis
= vanguard_C000012238Member
Total Annual Fund Operating Expenses 0.11%rr_NetExpensesOverAssets
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= vanguard_C000012238Member
[1]
[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.