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Shareholder Report
 12 Months Ended
Aug. 31, 2025
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name Vanguard Money Market Reserves
Entity Central Index Key 0000106830
Entity Investment Company Type N-1A
Document Period End Date Aug. 31, 2025
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 annual shareholder report contains important information about Vanguard Cash Reserves Federal Money Market Fund (the "Fund") for the period of September 1, 2024, to August 31, 2025.
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
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.
Additional Information Phone Number 800-662-7447
Additional Information Website https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature
Expenses [Text Block]

What were the Fund costs for the last year?

(based on a hypothetical $10,000 investment)

Share Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Admiral Shares
$10
0.10%
Expenses Paid, Amount $ 10
Expense Ratio, Percent 0.10%
AssetsNet $ 122,755,000,000
Holdings Count | Holding 273
Advisory Fees Paid, Amount $ 1,185,000
Additional Fund Statistics [Text Block]

Fund Statistics (as of August 31, 2025)

Fund Net Assets (in millions)
$122,755
Number of Portfolio Holdings
273
Total Investment Advisory Fees (in thousands)
$1,185
Holdings [Text Block]

Distribution by Effective Maturity % of Net Assets (as of August 31, 2025) 

1 to 7 Days
43.2%
8 to 30 Days
18.0%
31 to 60 Days
22.1%
61 to 90 Days
6.3%
91 to 180 Days
11.8%
Over 180 Days
0.1%
Other Assets and Liabilities—Net
(1.5%)

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.
Material Fund Change [Text Block]
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 annual shareholder report contains important information about Vanguard Federal Money Market Fund (the "Fund") for the period of September 1, 2024, to August 31, 2025.
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
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.
Additional Information Phone Number 800-662-7447
Additional Information Website https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature
Expenses [Text Block]

What were the Fund costs for the last year?

(based on a hypothetical $10,000 investment)

Share Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor Shares
$11
0.11%
Expenses Paid, Amount $ 11
Expense Ratio, Percent 0.11%
AssetsNet $ 361,670,000,000
Holdings Count | Holding 273
Advisory Fees Paid, Amount $ 3,351,000
Additional Fund Statistics [Text Block]

Fund Statistics (as of August 31, 2025)

Fund Net Assets (in millions)
$361,670
Number of Portfolio Holdings
273
Total Investment Advisory Fees (in thousands)
$3,351
Holdings [Text Block]

Distribution by Effective Maturity % of Net Assets (as of August 31, 2025) 

1 to 7 Days
44.6%
8 to 30 Days
17.5%
31 to 60 Days
21.5%
61 to 90 Days
6.0%
91 to 180 Days
11.8%
Over 180 Days
0.1%
Other Assets and Liabilities—Net
(1.5%)

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.
Material Fund Change [Text Block]
Updated Prospectus Phone Number 800-662-7447
Updated Prospectus Web Address https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature