Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Feb. 26, 2021
Retail | Vanguard Municipal Money Market Fund
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<span style="color:#000000;font-family:Arial;font-size:13pt;font-weight:bold;">Vanguard Municipal Money Market Fund</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to provide current income that is exempt from federal personal income taxes while maintaining liquidity and a stable share price of $1.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Fees and Expenses</span>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	<span style="color:#000000;font-family:Arial;font-size:8.5pt;font-weight:bold;margin-left:0%;">Shareholder Fees</span> <br/><span style="color:#000000;font-family:Arial;font-size:8.5pt;">(Fees paid directly from your investment)</span>
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<span style="color:#000000;font-family:Arial;font-size:8.5pt;font-weight:bold;margin-left:0%;">Annual Fund Operating Expenses</span> <br/><span style="color:#000000;font-family:Arial;font-size:8.5pt;">(Expenses that you pay each year as a percentage of the value of your investment)</span>
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Arial;font-size:9.5pt;margin-left:0%;">Example</span>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. This example assumes that the Fund provides a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you were to redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund invests in a variety of high-quality, short-term municipal securities. To be considered high quality, a security must be determined by Vanguard to present minimal credit risk based in part on a consideration of maturity, portfolio diversification, portfolio liquidity, and credit quality. The Fund invests in securities with effective maturities of 397 days or less, maintains a dollar-weighted average maturity of 60 days or less, and maintains a dollar-weighted average life of 120 days or less.
Risk [Heading]	rr_RiskHeading	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Principal Risks</span>
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The Fund is designed for investors with a low tolerance for risk; however, the Fund is subject to the following risks, which could affect the Fund's performance, and the level of risk may vary based on market conditions:•  Income risk , which is the chance that the Fund’s income will decline because of falling interest rates. Because the Fund’s income is based on short-term interest rates—which can fluctuate significantly over short periods—income risk is expected to be high. A low or negative interest rate environment will adversely affect the Fund's return. Low or negative interest rates, depending on their duration and severity, could prevent the Fund from, among other things, providing a positive yield and/or maintaining a stable share price of $1.•  Credit risk , which is the chance that the issuer of a security will fail to pay interest or principal in a timely manner or that negative perceptions of the issuer’s ability to make such payments will cause the price of that security to decline. Credit risk should be very low for the Fund because it invests primarily in securities that are considered to be of high quality.•  Manager risk , which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.•  Tax risk , which is the chance that all or a portion of the tax-exempt income from municipal bonds held by the Fund will be declared taxable, possibly with retroactive effect, because of unfavorable changes in tax laws, adverse interpretations by the Internal Revenue Service or state or local tax authorities, or noncompliant conduct of a bond issuer.•  Structured products risk . The Fund may invest in derivatives and structured products such as tender option bonds and long-term municipal securities combined with a demand feature (e.g., variable rate demand notes or VRDNs), which may involve risks different from, and possibly greater than, those of investments directly in the underlying securities or assets.You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. The Fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund's sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.
Risk Lose Money [Text]	rr_RiskLoseMoney	<span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">You could lose money by investing in the Fund.</span>
Risk Money Market Fund May Impose Fees Or Suspend Sales [Text]	rr_RiskMoneyMarketFundMayImposeFeesOrSuspendSales	<span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">The Fund may impose a fee upon sale of your </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors.</span>
Risk Not Insured [Text]	rr_RiskNotInsured	<span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;"> An investment in the Fund is not insured or guaranteed by the </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">Federal Deposit Insurance Corporation or any other government agency. </span>
Risk Money Market Fund Sponsor May Not Provide Support [Text]	rr_RiskMoneyMarketFundSponsorMayNotProvideSupport	<span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">The Fund's sponsor has no legal obligation to provide financial support to </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.</span>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0%;">Annual Total Returns</span>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table 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 comparative benchmark, which has investment characteristics similar to those of the Fund. Returns for the Municipal 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 or by calling Vanguard toll-free at 800-662-7447.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	<span style="color:#000000;font-family:Arial;font-size:9.5pt;">The following bar chart and table 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 comparative benchmark, which has investment characteristics similar to those of the Fund.</span>
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	<span style="color:#000000;font-family:Arial;font-size:9.5pt;">800-662-7447</span>
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	<span style="color:#000000;font-family:Arial;font-size:9.5pt;font-style:italic;">vanguard.com/performance</span>
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<span style="color:#000000;font-family:Arial;font-size:9.5pt;">Keep in mind that </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;">the Fund's past performance does not indicate how the Fund will perform in the future.</span>
Bar Chart [Heading]	rr_BarChartHeading	<span style="color:#000000;font-family:Arial;font-size:8pt;font-weight:bold;">Annual Total Returns — Vanguard Municipal Money Market Fund Investor Shares</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest and lowest returns for a calendar quarter were:
Performance Table Heading	rr_PerformanceTableHeading	<span style="color:#000000;font-family:Arial;font-size:8.5pt;font-weight:bold;">Average Annual Total Returns for Periods Ended December 31, 2020</span>
Retail | Vanguard Municipal Money Market Fund | Investor Shares
Risk Return Abstract	rr_RiskReturnAbstract
Purchase Fee	rr_MaximumCumulativeSalesChargeOverOther	none
Sales Charge (Load) Imposed on Purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Sales Charge (Load) Imposed on Reinvested Dividends	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption Fee	rr_RedemptionFeeOverRedemption	none
Account Service Fee Per Year (for certain fund account balances below $10,000)	rr_MaximumAccountFee	$ 20
Management Fees	rr_ManagementFeesOverAssets	0.14%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.15%
1 Year	rr_ExpenseExampleYear01	$ 15
3 Years	rr_ExpenseExampleYear03	48
5 Years	rr_ExpenseExampleYear05	85
10 Years	rr_ExpenseExampleYear10	$ 192
2011	rr_AnnualReturn2011	0.06%
2012	rr_AnnualReturn2012	0.04%
2013	rr_AnnualReturn2013	0.01%
2014	rr_AnnualReturn2014	0.01%
2015	rr_AnnualReturn2015	0.01%
2016	rr_AnnualReturn2016	0.33%
2017	rr_AnnualReturn2017	0.74%
2018	rr_AnnualReturn2018	1.31%
2019	rr_AnnualReturn2019	1.40%
2020	rr_AnnualReturn2020	0.50%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial;font-size:8pt;padding-left:0.0%;">Highest</span>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.40%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial;font-size:8pt;padding-left:0.0%;">Lowest</span>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2014
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	none
1 Year	rr_AverageAnnualReturnYear01	0.50%
5 Years	rr_AverageAnnualReturnYear05	0.86%
10 Years	rr_AverageAnnualReturnYear10	0.44%
Retail | Vanguard Municipal Money Market Fund | Tax-Exempt Money Market Funds Average
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.34%
5 Years	rr_AverageAnnualReturnYear05	0.58%
10 Years	rr_AverageAnnualReturnYear10	0.29%