Vanguard Cash Reserves Federal Money Market Fund Performance Management - Retail Prospectus [Member] - Vanguard Cash Reserves Federal Money Market Fund	Aug. 31, 2025
Prospectus [Line Items]
Bar Chart and Performance Table [Heading]	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Annual Total Returns</span>
Performance Narrative [Text Block]	Effective September 29, 2020, the Fund changed its investment strategy and name, and changed its designation to a government money market fund. Performance for the periods prior to September 29, 2020, is based on the investment strategy utilized by the Fund prior to September 29, 2020, under the name Vanguard Prime Money Market Fund. The following bar chart and table show the Fund’s historical performance and are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant peer group average. Returns for the U.S. Government Money Market Funds Average are derived from data provided by Lipper, a Thomson Reuters Company. Keep in mind that the Fund’s past performance does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance.
Performance Past Does Not Indicate Future [Text]	<span style="font-family:Arial;font-size:9.5pt;">Keep in mind that the Fund’s past </span><span style="font-family:Arial;font-size:9.5pt;">performance does not indicate how the Fund will perform in the future.</span>
Performance Information Illustrates Variability of Returns [Text]	<span style="font-family:Arial;font-size:9.5pt;">The following bar chart and table </span><span style="font-family:Arial;font-size:9.5pt;">show the Fund’s historical performance and are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant peer group average.</span>
Bar Chart [Heading]	<span style="font-family:Arial;font-size:8pt;font-weight:bold;">Annual Total Returns — Vanguard Cash Reserves Federal Money Market Fund Admiral Shares</span><span style="font-family:Arial;font-size:5pt;font-weight:bold;position:relative;top:-3.25pt;">1</span>
Bar Chart Closing [Text Block]	During the periods shown in the bar chart, the highest and lowest returns for a calendar quarter were:
Performance Table Heading	<span style="font-family:Arial;font-size:8.5pt;font-weight:bold;">Average Annual Total Returns for Periods Ended December 31, 2024</span>
Performance Availability Website Address [Text]	<span style="font-family:Arial;font-size:9.5pt;font-style:italic;">vanguard.com/performance</span>
Admiral Shares
Prospectus [Line Items]
Year to Date Return, Label [Optional Text]	year-to-date return
Bar Chart, Year to Date Return	3.21%
Bar Chart, Year to Date Return, Date	Sep. 30, 2025
Highest Quarterly Return, Label [Optional Text]	<span style="color:#000000;font-family:Arial;font-size:8pt;margin-left:0.0pt;">Highest</span>
Highest Quarterly Return	1.34%
Highest Quarterly Return, Date	Dec. 31, 2023
Lowest Quarterly Return, Label [Optional Text]	<span style="color:#000000;font-family:Arial;font-size:8pt;margin-left:0.0pt;">Lowest</span>
Lowest Quarterly Return	none
Lowest Quarterly Return, Date	Jun. 30, 2021