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Shareholder Report
 6 Months Ended 12 Months Ended
Feb. 28, 2026
USD ($)
Holding
Aug. 31, 2025
Shareholder Report [Line Items]    
Document Type N-CSRS  
Amendment Flag false  
Registrant Name Vanguard Money Market Reserves  
Entity Central Index Key 0000106830  
Entity Investment Company Type N-1A  
Document Period End Date Feb. 28, 2026  
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report  
C000012240    
Shareholder Report [Line Items]    
Fund Name Cash Reserves Federal Money Market Fund  
Class Name Admiral™ Shares  
Trading Symbol VMRXX  
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Cash Reserves Federal Money Market Fund (the "Fund") for the period of September 1, 2025, to February 28, 2026.  
Additional Information [Text Block] You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.  
Material Fund Change Notice [Text Block] The report describes changes to the Fund that occurred during the reporting period.  
Additional Information Phone Number <span style="white-space: nowrap; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto;"> 800-662-7447</span>  
Additional Information Website <span style="white-space: nowrap; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto;"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;"><span style="text-decoration: underline; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;">https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature</span></span></span>  
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Admiral Shares
$5
0.10%Footnote Reference1
FootnoteDescription
Footnote1
Annualized.
  
Expenses Paid, Amount $ 5  
Expense Ratio, Percent [1] 0.10%  
Material Change Date   Aug. 31, 2025
AssetsNet $ 120,752,000,000  
Holdings Count | Holding 274  
Additional Fund Statistics [Text Block]

Fund Statistics (as of February 28, 2026)

Table Summary
Fund Net Assets (in millions)
$120,752
Number of Portfolio Holdings
274
  
Holdings [Text Block]

Distribution by Effective Maturity % of Net Assets (as of February 28, 2026) 

Table Summary
1 to 7 Days
40.1%
8 to 30 Days
12.5%
31 to 60 Days
27.0%
61 to 90 Days
10.8%
91 to 180 Days
11.2%
Over 180 Days
2.0%
Other Assets and Liabilities—Net
(3.6%)

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.

  
Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

  

This is a summary of certain changes to the Fund since August 31, 2025. For more complete information, you may review the Fund’s prospectus, at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature or upon request at 800-662-7447.

  
Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

  
Summary of Change Legend [Text Block]

This is a summary of certain changes to the Fund since August 31, 2025. For more complete information, you may review the Fund’s prospectus, at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature or upon request at 800-662-7447.

  
Updated Prospectus Phone Number 800-662-7447  
Updated Prospectus Web Address https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature  
C000012238    
Shareholder Report [Line Items]    
Fund Name Federal Money Market Fund  
Class Name Investor Shares  
Trading Symbol VMFXX  
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Federal Money Market Fund (the "Fund") for the period of September 1, 2025, to February 28, 2026.  
Additional Information [Text Block] You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.  
Material Fund Change Notice [Text Block] The report describes changes to the Fund that occurred during the reporting period.  
Additional Information Phone Number <span style="white-space: nowrap; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto;"> 800-662-7447</span>  
Additional Information Website <span style="white-space: nowrap; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto;"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;"><span style="text-decoration: underline; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;">https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature</span></span></span>  
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor Shares
$6
0.11%Footnote Reference1
FootnoteDescription
Footnote1
Annualized.
  
Expenses Paid, Amount $ 6  
Expense Ratio, Percent [2] 0.11%  
Material Change Date   Aug. 31, 2025
AssetsNet $ 374,221,000,000  
Holdings Count | Holding 274  
Additional Fund Statistics [Text Block]

Fund Statistics (as of February 28, 2026)

Table Summary
Fund Net Assets (in millions)
$374,221
Number of Portfolio Holdings
274
  
Holdings [Text Block]

Distribution by Effective Maturity % of Net Assets (as of February 28, 2026) 

Table Summary
1 to 7 Days
42.1%
8 to 30 Days
11.5%
31 to 60 Days
26.3%
61 to 90 Days
9.9%
91 to 180 Days
11.8%
Over 180 Days
2.0%
Other Assets and Liabilities—Net
(3.6%)

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.

  
Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

  

This is a summary of certain changes to the Fund since August 31, 2025. For more complete information, you may review the Fund’s prospectus, at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature or upon request at 800-662-7447.

  
Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

  
Summary of Change Legend [Text Block]

This is a summary of certain changes to the Fund since August 31, 2025. For more complete information, you may review the Fund’s prospectus, at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature or upon request at 800-662-7447.

  
Updated Prospectus Phone Number 800-662-7447  
Updated Prospectus Web Address https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature  
[1] Annualized.
[2] Annualized.