Annual Total Returns (Vanguard Prime Money Market Fund - Institutional Shares Institutional) (Vanguard Prime Money Market Fund, Vanguard Prime Money Market Fund - Institutional Shares)	12 Months Ended
Aug. 31, 2014
Vanguard Prime Money Market Fund \| Vanguard Prime Money Market Fund - Institutional Shares
Annual Total Return
2013	0.06%
2012	0.11%
2011	0.14%
2010	0.20%
2009	0.68%
2008	2.93%
2007	5.30%
2006	5.08%
2005	3.21%
2004	1.33%

If the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).

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