| Shareholder Report | 12 Months Ended |
| Aug. 31, 2024 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, 2024 |
| 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, 2023, to August 31, 2024. |
| 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 | $ 120,164,000,000 |
| Holdings Count | Holding | 272 |
| Advisory Fees Paid, Amount | $ 727,000 |
| Additional Fund Statistics [Text Block] | Fund Statistics (as of August 31, 2024 Fund Net Assets (in millions) $120,164 Number of Portfolio Holdings 272 Total Investment Advisory Fees (in thousands) $727 |
| Holdings [Text Block] | This table reflects the Fund's investments, including short-term investments and other assets and liabilities. Distribution by Effective Maturity % of Net Assets (as of August 31, 2024 1 to 7 Days 65.5% 8 to 30 Days 9.9% 31 to 60 Days 9.9% 61 to 90 Days 9.0% 91 to 180 Days 7.4% Other Assets and Liabilities—Net (1.7%) |
| Material Fund Change [Text Block] | |
| 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, 2023, to August 31, 2024. |
| 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 | $ 310,399,000,000 |
| Holdings Count | Holding | 268 |
| Advisory Fees Paid, Amount | $ 1,824,000 |
| Additional Fund Statistics [Text Block] | Fund Statistics (as of August 31, 2024 Fund Net Assets (in millions) $310,399 Number of Portfolio Holdings 268 Total Investment Advisory Fees (in thousands) $1,824 |
| Holdings [Text Block] | This table reflects the Fund's investments, including short-term investments and other assets and liabilities. Distribution by Effective Maturity % of Net Assets (as of August 31, 2024 1 to 7 Days 68.8% 8 to 30 Days 7.9% 31 to 60 Days 9.1% 61 to 90 Days 8.5% 91 to 180 Days 7.4% Other Assets and Liabilities—Net (1.7%) |
| Material Fund Change [Text Block] | |
| Updated Prospectus Web Address | https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature |
