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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName PRUDENTIAL NATIONAL MUNI FUND, INC.
Prospectus Date rr_ProspectusDate Dec. 04, 2017
PRUDENTIAL NATIONAL MUNI FUND, INC.  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading FUND SUMMARY
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the Fund is to seek a high level of current income exempt from federal income taxes.
Expense [Heading] rr_ExpenseHeading FUND FEES AND EXPENSES
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The tables below describe the sales charges, fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and an eligible group of related investors purchase, or agree to purchase in the future, $100,000 or more in shares of the Fund or other funds in the Prudential mutual funds. More information about these discounts as well as other waivers or discounts is available from your financial professional and is explained in Reducing or Waiving Class A's and Class C's Sales Charges on page 26 of the Fund's Prospectus, Appendix A: Waivers and Discounts Available From Certain Financial Intermediaries on page 47 of the Fund's Prospectus and in Rights of Accumulation on page 47 of the Fund's Statement of Additional Information (SAI).
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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2019
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 higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the Fund's most recent fiscal year, the Fund's portfolio turnover rate was 33% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 33.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and an eligible group of related investors purchase, or agree to purchase in the future, $100,000 or more in shares of the Fund or other funds in the Prudential mutual funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other expenses are based on estimates.
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It assumes that you invest $10,000 in the Fund for the time periods indicated and then, except as indicated, redeem all your shares at the end of those periods. It assumes a 5% return on your investment each year, that the Fund's operating expenses remain the same (except that fee waivers or reimbursements, if any, are only reflected in the 1-Year figures) and that all dividends and distributions are reinvested. Your actual costs may be higher or lower.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If Shares Are Redeemed
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If Shares Are Not Redeemed
Strategy [Heading] rr_StrategyHeading INVESTMENTS, RISKS AND PERFORMANCE

Principal Investment Strategies.
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund invests, under normal circumstances, at least 80% of the Fund's investable assets in obligations the income from which is exempt from federal income tax, that is, municipal obligations. The term “investable assets” in this prospectus refers to the Fund's net assets plus any borrowings for investment purposes. The Fund's investable assets will be less than its total assets to the extent that it has borrowed money for non-investment purposes, such as to meet anticipated redemptions.

The Fund's investments permitted by this policy may include certain municipal bonds, the interest on which is subject to the federal alternative minimum tax (AMT). The Fund's portfolio consists primarily of investment grade long-term municipal bonds, which are bonds rated Baa3 or higher by Moody's Investors Service (Moody's), and BBB- or higher by S&P Global Ratings (S&P), or comparably rated by another nationally recognized statistical rating organization (NRSRO), and unrated debt obligations that the investment subadviser believes are comparable in quality. The Fund may invest up to 15% of the Fund's investable assets in “below-investment grade” or high-yield municipal debt obligations, commonly known as junk bonds. Below-investment grade securities are rated below Baa3 by Moody's and below BBB- by S&P, or comparably rated by another NRSRO, and are considered speculative. The Fund may invest in obligations the interest and/or principal payments on which are insured by the bond insurers or other parties.

In seeking to achieve the Fund's investment objective, the investment subadviser will purchase securities that it believes represent the best values based on yield, maturity, issue, quality characteristics and expectations regarding economic and political developments, including movements in interest rates and demand for municipal bonds.
Risk [Heading] rr_RiskHeading Principal Risks.
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock All investments have risks to some degree. An investment in the Fund is not guaranteed to achieve its investment objective; is not a deposit with a bank; is not insured, endorsed or guaranteed by the Federal Deposit Insurance Corporation or any other government agency; and is subject to investment risks, including possible loss of your original investment.

Municipal Bonds Risk. Municipal bonds are subject to credit risk, market risk and interest rate risk. The Fund's holdings, share price, yield and total return may also fluctuate in response to municipal bond market movements. Municipal bonds are also subject to the risk that potential future legislative changes could affect the market for and value of municipal bonds, which may adversely affect the Fund's yield or the value of the Fund's investments in municipal bonds. Certain municipal bonds with principal and interest payments that are made from the revenues of a specific project or facility, and not general tax revenues, may have increased risks. Factors affecting the project or facility, such as local business or economic conditions, could have a significant effect on the project's ability to make payments of principal and interest on these securities. Municipal securities of a particular state are vulnerable to events adversely affecting that state, including economic, political and regulatory occurrences, court decisions, terrorism and catastrophic natural disasters, such as hurricanes or earthquakes. Many municipal bonds are also subject to prepayment risk, which is the risk that when interest rates fall, issuers may redeem a security by repaying it early, which may reduce the Fund's income if the proceeds are reinvested at a lower interest rate. In addition, income from municipal bonds could be declared taxable because of non-compliant conduct of a bond issuer.

Insured Municipal Bonds Risk. The Fund may purchase municipal bonds that are insured to attempt to reduce credit risk. Although insurance coverage reduces credit risk by providing that the insurer will make timely payment of interest and/or principal, it does not provide protection against market fluctuations of insured bonds or fluctuations in the price of the shares of the Fund. An insured municipal bond fluctuates in value largely based on factors relating to the insurer's creditworthiness or ability to satisfy its obligations. The Fund cannot be certain that any insurance company will make the payments it guarantees.

Liquidity Risk. The Fund may invest in instruments that trade in lower volumes and are less liquid than other investments. Liquidity risk exists when particular investments made by the Fund are difficult to purchase or sell. Liquidity risk also includes the risk that the Fund may make investments that may become less liquid in response to market developments or adverse investor perceptions. If the Fund is forced to sell these investments to pay redemption proceeds or for other reasons, the Fund may lose money. In addition, when there is no willing buyer and investments cannot be readily sold at the desired time or price, the Fund may have to accept a lower price or may not be able to sell the instrument at all. The reduction in dealer market-making capacity in the fixed-income markets that has occurred in recent years also has the potential to reduce liquidity. An inability to sell a portfolio position can adversely affect the Fund's value or prevent the Fund from being able to take advantage of other investment opportunities.

Junk Bonds Risk. High-yield, high-risk bonds have predominantly speculative characteristics, including particularly high credit risk. Junk bonds tend to be less liquid than higher-rated securities. The liquidity of particular issuers or industries within a particular investment category may shrink or disappear suddenly and without warning. The non-investment grade bond market can experience sudden and sharp price swings and become illiquid due to a variety of factors, including changes in economic forecasts, stock market activity, large sustained sales by major investors, a high profile default or a change in the market's psychology.

Interest Rate Risk. The value of your investment may go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term or duration securities. When interest rates fall, the issuers of debt obligations may prepay principal more quickly than expected, and the Fund may be required to reinvest the proceeds at a lower interest rate. This is referred to as “prepayment risk.” When interest rates rise, debt obligations may be repaid more slowly than expected, and the value of the Fund's holdings may fall sharply. This is referred to as “extension risk.” The Fund may face a heightened level of interest rate risk since the US Federal Reserve Board has ended its quantitative easing program and may continue to raise rates. The Fund may lose money if short-term or long-term interest rates rise sharply or in a manner not anticipated by the subadviser.

Credit Risk. This is the risk that the issuer, the guarantor or the insurer of a fixed-income security, or the counterparty to a contract may be unable or unwilling to make timely principal and interest payments or to otherwise honor its obligations. Additionally, the securities could lose value due to a loss of confidence in the ability of the issuer, guarantor, insurer or counterparty to pay back debt. The longer the maturity and the lower the credit quality of a bond, the more sensitive it is to credit risk.

Market Risk. Securities markets may be volatile and the market prices of the Fund’s securities may decline. Securities fluctuate in price based on changes in an issuer’s financial condition and overall market and economic conditions. If the market prices of the securities owned by the Fund fall, the value of your investment in the Fund will decline.

Management Risk. The value of your investment may decrease if judgments by the subadviser about the attractiveness, value or market trends affecting a particular security, industry or sector or about market movements are incorrect.

Market Events Risk. Events in the financial markets have resulted in, and may continue to result in, an unusually high degree of volatility, both in foreign and US markets. This market volatility, in addition to reduced liquidity in credit and fixed-income markets, may adversely affect issuers worldwide. Furthermore, the impact of policy and legislative changes in the US and other countries may not be fully known for some time. This environment could make identifying investment risks and opportunities especially difficult for the subadviser.

Risk of Increase in Expenses. Your actual cost of investing in the Fund may be higher than the expenses shown in the expense table for a variety of reasons. For example, expense ratios may be higher than those shown if average net assets decrease. Net assets are more likely to decrease and Fund expense ratios are more likely to increase when markets are volatile. Active and frequent trading of Fund securities can increase expenses.
Risk Lose Money [Text] rr_RiskLoseMoney and is subject to investment risks, including possible loss of your original investment.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not guaranteed to achieve its investment objective; is not a deposit with a bank; is not insured, endorsed or guaranteed by the Federal Deposit Insurance Corporation or any other government agency;
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance.
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The following bar chart shows the Fund's performance for Class A shares for each full calendar year of operations or for the last 10 calendar years, whichever is shorter. The following table shows the average annual returns of each of the Fund’s share classes and also compares the Fund’s performance with the average annual total returns of an index or other benchmark and a group of similar mutual funds. The bar chart and table demonstrate the risk of investing in the Fund by showing how returns can change from year to year.

Past performance (before and after taxes) does not mean that the Fund will achieve similar results in the future. Updated Fund performance information is available online at www.pgiminvestments.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following table shows the average annual returns of each of the Fund’s share classes and also compares the Fund’s performance with the average annual total returns of an index or other benchmark and a group of similar mutual funds. The bar chart and table demonstrate the risk of investing in the Fund by showing how returns can change from year to year.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Average annual total returns are not shown for Class Q shares, because Class Q shares are new. Performance for Class Q shares will be included after Class Q shares have been in existence for a full calendar year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.pgiminvestments.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) does not mean that the Fund will achieve similar results in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns (Class A Shares)1
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads These annual total returns do not include sales charges. If the sales charges were included, the annual total returns would be lower than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter: Worst Quarter:
7.44% 3rd Quarter 2009 -4.68% 4th Quarter 2010
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns % (including sales charges) (as of 12-31-16)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown only for the indicated share class. After-tax returns for other classes will vary due to differing sales charges and expenses.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock ° After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown only for the indicated share class. After-tax returns for other classes will vary due to differing sales charges and expenses.
PRUDENTIAL NATIONAL MUNI FUND, INC. | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.00%
Maximum deferred sales charge (load) (as a percentage of the lower of original purchase price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum sales charge (load) imposed on reinvested dividends and other distributions rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Exchange fee rr_ExchangeFeeOverRedemption none
Maximum account fee (accounts under $10,000) rr_MaximumAccountFee $ 15
Management fees rr_ManagementFeesOverAssets 0.48%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.11% [1]
Total annual Fund operating expenses rr_ExpensesOverAssets 0.84%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual Fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.84% [2]
1 Year rr_ExpenseExampleYear01 $ 482
3 Years rr_ExpenseExampleYear03 657
5 Years rr_ExpenseExampleYear05 847
10 Years rr_ExpenseExampleYear10 1,396
1 Year rr_ExpenseExampleNoRedemptionYear01 482
3 Years rr_ExpenseExampleNoRedemptionYear03 657
5 Years rr_ExpenseExampleNoRedemptionYear05 847
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,396
2007 rr_AnnualReturn2007 1.69% [3]
2008 rr_AnnualReturn2008 (6.10%) [3]
2009 rr_AnnualReturn2009 14.87% [3]
2010 rr_AnnualReturn2010 0.79% [3]
2011 rr_AnnualReturn2011 10.27% [3]
2012 rr_AnnualReturn2012 8.69% [3]
2013 rr_AnnualReturn2013 (4.38%) [3]
2014 rr_AnnualReturn2014 9.85% [3]
2015 rr_AnnualReturn2015 3.00% [3]
2016 rr_AnnualReturn2016 0.30% [3]
Year to Date Return, Label rr_YearToDateReturnLabel The total return for Class A shares from January 1, 2017 to September 30, 2017
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2017
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 3.94%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.44%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (4.68%)
One Year rr_AverageAnnualReturnYear01 (3.71%)
Five Years rr_AverageAnnualReturnYear05 2.51%
Ten Years rr_AverageAnnualReturnYear10 3.28%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Class B  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of the lower of original purchase price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther 5.00%
Maximum sales charge (load) imposed on reinvested dividends and other distributions rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Exchange fee rr_ExchangeFeeOverRedemption none
Maximum account fee (accounts under $10,000) rr_MaximumAccountFee $ 15
Management fees rr_ManagementFeesOverAssets 0.48%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.23% [1]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.21%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual Fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.21% [2]
1 Year rr_ExpenseExampleYear01 $ 623
3 Years rr_ExpenseExampleYear03 684
5 Years rr_ExpenseExampleYear05 765
10 Years rr_ExpenseExampleYear10 1,315
1 Year rr_ExpenseExampleNoRedemptionYear01 123
3 Years rr_ExpenseExampleNoRedemptionYear03 384
5 Years rr_ExpenseExampleNoRedemptionYear05 665
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,315
One Year rr_AverageAnnualReturnYear01 (4.79%)
Five Years rr_AverageAnnualReturnYear05 2.92%
Ten Years rr_AverageAnnualReturnYear10 3.44%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of the lower of original purchase price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum sales charge (load) imposed on reinvested dividends and other distributions rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Exchange fee rr_ExchangeFeeOverRedemption none
Maximum account fee (accounts under $10,000) rr_MaximumAccountFee $ 15
Management fees rr_ManagementFeesOverAssets 0.48%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.16% [1]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.64%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual Fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.64% [2]
1 Year rr_ExpenseExampleYear01 $ 267
3 Years rr_ExpenseExampleYear03 517
5 Years rr_ExpenseExampleYear05 892
10 Years rr_ExpenseExampleYear10 1,944
1 Year rr_ExpenseExampleNoRedemptionYear01 167
3 Years rr_ExpenseExampleNoRedemptionYear03 517
5 Years rr_ExpenseExampleNoRedemptionYear05 892
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,944
One Year rr_AverageAnnualReturnYear01 (1.44%)
Five Years rr_AverageAnnualReturnYear05 2.58%
Ten Years rr_AverageAnnualReturnYear10 3.03%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Class Q  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of the lower of original purchase price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther none
Maximum sales charge (load) imposed on reinvested dividends and other distributions rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Exchange fee rr_ExchangeFeeOverRedemption none
Maximum account fee (accounts under $10,000) rr_MaximumAccountFee none
Management fees rr_ManagementFeesOverAssets 0.48%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 1.65% [1]
Total annual Fund operating expenses rr_ExpensesOverAssets 2.13%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (1.52%)
Total annual Fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.61% [2]
1 Year rr_ExpenseExampleYear01 $ 62
3 Years rr_ExpenseExampleYear03 520
5 Years rr_ExpenseExampleYear05 1,004
10 Years rr_ExpenseExampleYear10 2,342
1 Year rr_ExpenseExampleNoRedemptionYear01 62
3 Years rr_ExpenseExampleNoRedemptionYear03 520
5 Years rr_ExpenseExampleNoRedemptionYear05 1,004
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,342
One Year rr_AverageAnnualReturnYear01 [4]
Five Years rr_AverageAnnualReturnYear05 [4]
Ten Years rr_AverageAnnualReturnYear10 [4]
PRUDENTIAL NATIONAL MUNI FUND, INC. | Class Z  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of the lower of original purchase price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther none
Maximum sales charge (load) imposed on reinvested dividends and other distributions rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Exchange fee rr_ExchangeFeeOverRedemption none
Maximum account fee (accounts under $10,000) rr_MaximumAccountFee none [5]
Management fees rr_ManagementFeesOverAssets 0.48%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.13% [1]
Total annual Fund operating expenses rr_ExpensesOverAssets 0.61%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual Fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.61% [2]
1 Year rr_ExpenseExampleYear01 $ 62
3 Years rr_ExpenseExampleYear03 195
5 Years rr_ExpenseExampleYear05 340
10 Years rr_ExpenseExampleYear10 762
1 Year rr_ExpenseExampleNoRedemptionYear01 62
3 Years rr_ExpenseExampleNoRedemptionYear03 195
5 Years rr_ExpenseExampleNoRedemptionYear05 340
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 762
One Year rr_AverageAnnualReturnYear01 0.55%
Five Years rr_AverageAnnualReturnYear05 3.60%
Ten Years rr_AverageAnnualReturnYear10 3.95%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Return After Taxes on Distributions | Class A  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 (3.73%)
Five Years rr_AverageAnnualReturnYear05 2.50%
Ten Years rr_AverageAnnualReturnYear10 3.26%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Return After Taxes on Distribution and Sale of Fund Shares | Class A  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 (0.65%)
Five Years rr_AverageAnnualReturnYear05 2.77%
Ten Years rr_AverageAnnualReturnYear10 3.39%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Bloomberg Barclays Municipal Bond Index (reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 0.25%
Five Years rr_AverageAnnualReturnYear05 3.28%
Ten Years rr_AverageAnnualReturnYear10 4.25%
PRUDENTIAL NATIONAL MUNI FUND, INC. | Lipper General & Insured Municipal Debt Funds Average (reflects no deduction for sales charges or taxes)  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 0.04%
Five Years rr_AverageAnnualReturnYear05 3.48%
Ten Years rr_AverageAnnualReturnYear10 3.58%
[1] Other expenses are based on estimates.
[2] PGIM Investments LLC (PGIM Investments) has contractually agreed, through December 31, 2019, to limit transfer agency, shareholder servicing, sub-transfer agency, and blue sky fees, as applicable, to the extent that such fees cause the Total Annual Fund Operating Expenses to exceed 0.61% of average daily net assets for Class Q shares. This contractual expense limitation excludes interest, brokerage, taxes (such as income and foreign withholding taxes, stamp duty and deferred tax expenses), acquired fund fees and expenses, extraordinary expenses, and certain other Fund expenses such as dividend and interest expense and broker charges on short sales. Fees and/or expenses waived and/or reimbursed by PGIM Investments may be recouped by PGIM Investments within the same fiscal year during which such waiver and/or reimbursement is made if such recoupment can be realized without exceeding the expense limit in effect at the time of the recoupment for that fiscal year. This expense limitation may not be terminated prior to December 31, 2019 without the prior approval of the Fund's Board of Directors.
[3] These annual total returns do not include sales charges. If the sales charges were included, the annual total returns would be lower than those shown. The total return for Class A shares from January 1, 2017 to September 30, 2017 was 3.94%.
[4] Average annual total returns are not shown for Class Q shares, because Class Q shares are new. Performance for Class Q shares will be included after Class Q shares have been in existence for a full calendar year.
[5] Direct Transfer Agent Accounts holding under $10,000 of Class Z shares are subject to the $15 fee.