Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	VANGUARD MUNICIPAL BOND FUNDS
Prospectus Date	rr_ProspectusDate	Feb. 23, 2017
Retail | Vanguard Tax-Exempt Bond Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Summary
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to track the performance of a benchmark index that measures the investment-grade segment of the U.S. municipal bond market.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses you may pay if you buy and hold Investor Shares or Admiral Shares of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (Fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense examples, reduce the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 8% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	8.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	Examples
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following examples are intended to help you compare the cost of investing in the Fund’s Investor Shares or Admiral Shares with the cost of investing in other mutual funds. They illustrate the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. These examples assume that the shares provide 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 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	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund employs an indexing investment approach designed to track the Standard & Poor's National AMT-Free Municipal Bond Index, which measures the performance of the investment-grade segment of the U.S. municipal bond market. This Index includes municipal bonds from issuers that are primarily state or local governments or agencies whose interest is exempt from U.S. federal income taxes and the federal alternative minimum tax (AMT). To be eligible for inclusion in the Index, each bond must have a rating of at least investment-grade, as determined by a nationally recognized statistical rating organization (e.g., at least BBB– by Fitch Ratings, Inc.); be denominated in U.S. dollars; and have a minimum par amount of $25 million. In addition, to be included in the Index, each bond must have a minimum term to maturity or call date greater than one calendar month. The Fund invests by sampling the Index, meaning that it holds a range of securities that, in the aggregate, approximates the full Index in terms of key risk factors and other characteristics. All of the Fund's investments will be selected through the sampling process, and at least 80% of the Fund's assets will be invested in securities held in the Index. Under normal circumstances, at least 80% of the Fund's assets will be invested in securities whose income will be exempt from federal income taxes and the federal alternative minimum tax.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The Fund is designed for investors with a low tolerance for risk, but you could still lose money by investing in it. The Fund is subject to the following risks, which could affect the Fund's performance: • Interest rate risk, which is the chance that bond prices will decline because of rising interest rates. • Income risk, which is the chance that the Fund's income will decline because of falling interest rates. • Call risk, which is the chance that during periods of falling interest rates, issuers of callable bonds may call (redeem) securities with higher coupon rates or interest rates before their maturity dates. The Fund would then lose any price appreciation above the bond's call price and would be forced to reinvest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund's income. Such redemptions and subsequent reinvestments would also increase the Fund's portfolio turnover rate. • Extension risk, which is the chance that during periods of rising interest rates, certain debt securities will be paid off substantially more slowly than originally anticipated, and the value of those securities may fall. • Credit risk, which is the chance that a bond issuer 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 bond to decline. In general, credit risk should be relatively low for the Fund because it invests primarily in bonds that are considered to be of high quality. • Index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund's target index. Index sampling risk for the Fund should be low to moderate. • Liquidity risk, which is the chance that the Fund may not be able to sell a security in a timely manner at a desired price. • 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. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	The Fund is designed for investors with a low tolerance for risk, but you could still lose money by investing in it.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Annual Total Returns
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 the performance of the Fund‘s Investor Shares (including annual fund operating expenses but excluding shareholder fees) in their first full calendar year. If applicable shareholder fees were reflected, returns would be less than those shown in the bar chart. The table shows how the average annual total returns of the share classes presented (including annual fund operating expenses and any applicable shareholder fees) compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. Keep in mind that the Fund’s past performance (before and after taxes) 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	The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows the performance of the Fund‘s Investor Shares (including annual fund operating expenses but excluding shareholder fees) in their first full calendar year. If applicable shareholder fees were reflected, returns would be less than those shown in the bar chart. The table shows how the average annual total returns of the share classes presented (including annual fund operating expenses and any applicable shareholder fees) compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-662-7447
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	vanguard.com/performance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	Keep in mind that the Fund’s past performance (before and after taxes) does not indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns — Vanguard Tax-Exempt Bond Index Fund Investor Shares
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest return for a calendar quarter was 2.59% (quarter ended June 30, 2016), and the lowest return for a quarter was –3.52% (quarter ended December 31, 2016).
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns for Periods Ended December 31, 2016
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	After-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	Please note that after-tax returns are shown only for the Investor Shares and may differ for each share class.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are shown only for the Investor Shares and may differ for each share class. After-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.
Retail | Vanguard Tax-Exempt Bond Index Fund | Investor Shares
Risk/Return:	rr_RiskReturnAbstract
Purchase Fee	rr_MaximumCumulativeSalesChargeOverOther	0.25%
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 (for certain fund account balances below $10,000)	rr_MaximumAccountFee	$ 20	[1]
Management Fees	rr_ManagementFeesOverAssets	0.14%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.05%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.19%
1 Year	rr_ExpenseExampleYear01	$ 44
3 Years	rr_ExpenseExampleYear03	86
5 Years	rr_ExpenseExampleYear05	132
10 Years	rr_ExpenseExampleYear10	267
1 Year	rr_ExpenseExampleNoRedemptionYear01	44
3 Years	rr_ExpenseExampleNoRedemptionYear03	86
5 Years	rr_ExpenseExampleNoRedemptionYear05	132
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 267
2016	rr_AnnualReturn2016	0.25%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2016
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	2.59%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(3.52%)
1 Year	rr_AverageAnnualReturnYear01	none	[2]
Since Inception	rr_AverageAnnualReturnSinceInception	1.57%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 21, 2015
Retail | Vanguard Tax-Exempt Bond Index Fund | Admiral Shares
Risk/Return:	rr_RiskReturnAbstract
Purchase Fee	rr_MaximumCumulativeSalesChargeOverOther	0.25%
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 (for certain fund account balances below $10,000)	rr_MaximumAccountFee	$ 20	[1]
Management Fees	rr_ManagementFeesOverAssets	0.06%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.03%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.09%
1 Year	rr_ExpenseExampleYear01	$ 34
3 Years	rr_ExpenseExampleYear03	54
5 Years	rr_ExpenseExampleYear05	76
10 Years	rr_ExpenseExampleYear10	140
1 Year	rr_ExpenseExampleNoRedemptionYear01	34
3 Years	rr_ExpenseExampleNoRedemptionYear03	54
5 Years	rr_ExpenseExampleNoRedemptionYear05	76
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 140
1 Year	rr_AverageAnnualReturnYear01	0.08%
Since Inception	rr_AverageAnnualReturnSinceInception	1.77%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 25, 2015
Retail | Vanguard Tax-Exempt Bond Index Fund | Return After Taxes on Distributions | Investor Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	none	[2]
Since Inception	rr_AverageAnnualReturnSinceInception	1.57%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 21, 2015
Retail | Vanguard Tax-Exempt Bond Index Fund | Return After Taxes on Distributions and Sale of Fund Shares | Investor Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.68%
Since Inception	rr_AverageAnnualReturnSinceInception	1.57%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 21, 2015
Retail | Vanguard Tax-Exempt Bond Index Fund | S&P National AMT-Free Municipal Bond Index (reflects no deduction for fees, expenses, or taxes) | Investor Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.36%
Since Inception	rr_AverageAnnualReturnSinceInception	1.84%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 21, 2015
Retail | Vanguard Tax-Exempt Bond Index Fund | S&P National AMT-Free Municipal Bond Index (reflects no deduction for fees, expenses, or taxes) | Admiral Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.36%
Since Inception	rr_AverageAnnualReturnSinceInception	1.92%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 25, 2015

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[2] 0.00%