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Class T Prospectus | Dreyfus AMT-Free Municipal Bond 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 as high a level of current income exempt from federal income tax as is consistent with the preservation of capital.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the 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 invest at least $250,000 in the fund. More information about sales charges, including such discounts, is available from your financial professional and in the Shareholder Guide section beginning on page 9 of the prospectus and in the How to Buy Shares section and the Additional Information About How to Buy Shares section beginning on page II-1 and page III-1, respectively, of the fund's Statement of Additional Information.
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 Mar. 31, 2018
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 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 most recent fiscal year, the fund's portfolio turnover rate was 8.21% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 8.21%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you invest at least $250,000 in the fund.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 250,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the fund for the time periods indicated and then hold or redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the fund's operating expenses remain the same. The one-year example and the first year of the three-, five- and ten-years examples are based on net operating expenses, which reflect the expense limitation by The Dreyfus Corporation. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

To pursue its goal, the fund normally invests substantially all of its net assets in municipal bonds that provide income exempt from federal income tax. Municipal bonds are debt securities or other obligations issued by states, territories and possessions of the United States (such as Puerto Rico, the U.S. Virgin Islands, Guam and the Northern Mariana Islands) and the District of Columbia and their political subdivisions, agencies and instrumentalities, or multistate agencies and authorities, and certain other specified securities, the interest from which is, in the opinion of bond counsel to the issuer, exempt from federal income tax. The fund also seeks to provide income exempt from the federal alternative minimum tax. The fund invests at least 65% of its assets in municipal bonds with an A or higher credit rating, or the unrated equivalent as determined by The Dreyfus Corporation. The fund may invest the remaining 35% of its assets in municipal bonds with a credit rating lower than A, including municipal bonds rated below investment grade ("high yield" or "junk" bonds), or the unrated equivalent as determined by The Dreyfus Corporation.


The dollar-weighted average maturity of the fund's portfolio normally exceeds ten years, but the fund may invest without regard to maturity.


The portfolio managers focus on identifying undervalued sectors and securities. To select municipal bonds for the fund, the portfolio managers use fundamental credit analysis to estimate the relative value and attractiveness of various sectors and securities and actively trade among various sectors based on their apparent relative values.


Although the fund seeks to provide income exempt from federal income tax, the fund may invest temporarily in taxable bonds, including when the portfolio managers believe acceptable municipal bonds are not available for investment. During such periods, the fund may not achieve its investment objective.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. It is not a complete investment program. The fund's share price fluctuates, sometimes dramatically, which means you could lose money.


· Municipal securities risk. The amount of public information available about municipal securities is generally less than that for corporate equities or bonds. Special factors, such as legislative changes, and state and local economic and business developments, may adversely affect the yield and/or value of the fund's investments in municipal securities. Other factors include the general conditions of the municipal securities market, the size of the particular offering, the maturity of the obligation and the rating of the issue. Changes in economic, business or political conditions relating to a particular municipal project, municipality, or state, territory or possession of the United States in which the fund invests may have an impact on the fund's share price.


· Interest rate risk. Prices of bonds and other fixed rate fixed-income securities tend to move inversely with changes in interest rates. Typically, a rise in rates will adversely affect fixed-income securities and, accordingly, will cause the value of the fund's investments in these securities to decline. During periods of very low interest rates, which occur from time to time due to market forces or actions of governments and/or their central banks, including the Board of Governors of the Federal Reserve System in the U.S., the fund may be subject to a greater risk of principal decline from rising interest rates. When interest rates fall, the fund's investments in new securities may be at lower yields and may reduce the fund's income. The magnitude of these fluctuations in the market price of fixed-income securities is generally greater for securities with longer effective maturities and durations because such instruments do not mature, reset interest rates or become callable for longer periods of time. The change in the value of a fixed-income security or portfolio can be approximated by multiplying its duration by a change in interest rates. For example, the market price of a fixed-income security with a duration of three years would be expected to decline 3% if interest rates rose 1%. Conversely, the market price of the same security would be expected to increase 3% if interest rates fell 1%. Risks associated with rising interest rates are heightened given that interest rates in the United States and other countries currently are at or near historic lows. Unlike investment grade bonds, however, the prices of high yield bonds may fluctuate unpredictably and not necessarily inversely with changes in interest rates.


· Credit risk. Failure of an issuer of a security to make timely interest or principal payments when due, or a decline or perception of a decline in the credit quality of the security, can cause the security's price to fall. The lower a security's credit rating, the greater the chance that the issuer of the security will default or fail to meet its payment obligations.


· High yield securities risk. High yield ("junk") securities involve greater credit risk, including the risk of default, than investment grade securities, and are considered predominantly speculative with respect to the issuer's ability to make principal and interest payments. The prices of high yield securities can fall in response to bad news about the issuer or its industry, or the economy in general, to a greater extent than those of higher rated securities.


· Liquidity risk. When there is little or no active trading market for specific types of securities, it can become more difficult to sell the securities in a timely manner at or near their perceived value. In such a market, the value of such securities and the fund's share price may fall dramatically, even during periods of declining interest rates. The secondary market for certain municipal bonds tends to be less well developed or liquid than many other securities markets, which may adversely affect the fund's ability to sell such municipal bonds at attractive prices. Investments that are illiquid or that trade in lower volumes may be more difficult to value. The market for below investment grade securities may be less liquid and therefore these securities may be harder to value or sell at an acceptable price, especially during times of market volatility or decline. Liquidity risk also may refer to the risk that the fund will not be able to pay redemption proceeds within the allowable time period stated in this prospectus because of unusual market conditions, an unusually high volume of redemption requests, or other reasons. To meet redemption requests, the fund may be forced to sell securities at an unfavorable time and/or under unfavorable conditions, which may adversely affect the fund's share price.


· Non-diversification risk. The fund is non-diversified, which means that the fund may invest a relatively high percentage of its assets in a limited number of issuers. Therefore, the fund's performance may be more vulnerable to changes in the market value of a single issuer or group of issuers and more susceptible to risks associated with a single economic, political or regulatory occurrence than a diversified fund.

Risk Lose Money [Text] rr_RiskLoseMoney The fund's share price fluctuates, sometimes dramatically, which means you could lose money.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus The fund is non-diversified, which means that the fund may invest a relatively high percentage of its assets in a limited number of issuers. Therefore, the fund's performance may be more vulnerable to changes in the market value of a single issuer or group of issuers and more susceptible to risks associated with a single economic, political or regulatory occurrence than a diversified fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the performance of the fund's Class T shares from year to year. Sales charges are not reflected in the bar chart, and, if those charges were included, returns would have been less than those shown. The table compares the average annual total returns of the fund's Class T shares to those of a broad measure of market performance. The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. More recent performance information may be available at www.dreyfus.com.


The historical performance of the fund's Class A shares, which are not offered in this prospectus, is used to calculate the performance of the fund's Class T shares shown in the bar chart and table. Since the fund's Class T shares are new, past performance information is not available for Class T shares as of the date of this prospectus. Each share class is invested in the same portfolio of securities, and the annual returns would have differed only to the extent that the classes do not have the same charges and expenses. The performance figures in the table have been adjusted to reflect the sales load applicable to the fund's Class T shares. The performance figures have not been adjusted to reflect applicable class fees and expenses.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Since the fund's Class T shares are new, past performance information is not available for Class T shares as of the date of this prospectus.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dreyfus.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Total Returns as of 12/31 each year (%) Class T*
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges are not reflected in the bar chart, and, if those charges were included, returns would have been less than those shown.
Bar Chart Footnotes [Text Block] rr_BarChartFootnotesTextBlock

* Reflects the performance of the fund's Class A shares, which are offered in a separate prospectus. Such performance figures have not been adjusted to reflect applicable class fees and expenses.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q3, 2009: 8.61%


Worst Quarter
Q4, 2010: -5.13%
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The historical performance of the fund's Class A shares, which are not offered in this prospectus, is used to calculate the performance of the fund's Class T shares shown in the bar chart and table.
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 8.61%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.13%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deduction for fees, expenses or taxes
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 Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through U.S. tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher Returns after taxes on distributions and sale of fund shares may be higher than returns before taxes or returns after taxes on distributions due to an assumed tax benefit from losses on a sale of the fund’s shares at the end of the period.
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 the investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through U.S. tax-deferred arrangements such as 401(k) plans or individual retirement accounts. Returns after taxes on distributions and sale of fund shares may be higher than returns before taxes or returns after taxes on distributions due to an assumed tax benefit from losses on a sale of the fund’s shares at the end of the period.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (as of 12/31/16)
Class T Prospectus | Dreyfus AMT-Free Municipal Bond Fund | Bloomberg Barclays U.S. Municipal Bond Index reflects no deduction for fees, expenses or taxes  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.25%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.28%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.25%
Class T Prospectus | Dreyfus AMT-Free Municipal Bond Fund | Class T  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum deferred sales charge (load) (as a percentage of lower of purchase or sale price) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution/service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.09%
Total annual fund operating expenses rr_ExpensesOverAssets 0.94%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.24%) [1]
Total annual fund operating expenses (after fee waiver and/or expense reimbursement) rr_NetExpensesOverAssets 0.70%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 320
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 519
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 734
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,354
Class T Prospectus | Dreyfus AMT-Free Municipal Bond Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Annual Return 2007 rr_AnnualReturn2007 2.07%
Annual Return 2008 rr_AnnualReturn2008 (6.72%)
Annual Return 2009 rr_AnnualReturn2009 14.92%
Annual Return 2010 rr_AnnualReturn2010 1.52%
Annual Return 2011 rr_AnnualReturn2011 11.00%
Annual Return 2012 rr_AnnualReturn2012 7.81%
Annual Return 2013 rr_AnnualReturn2013 (3.63%)
Annual Return 2014 rr_AnnualReturn2014 10.24%
Annual Return 2015 rr_AnnualReturn2015 3.69%
Annual Return 2016 rr_AnnualReturn2016 (0.33%)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (2.79%) [2]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.91% [2]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.59% [2]
Class T Prospectus | Dreyfus AMT-Free Municipal Bond Fund | Class A | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (2.79%) [2]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.91% [2]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.59% [2]
Class T Prospectus | Dreyfus AMT-Free Municipal Bond Fund | Class A | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (0.33%) [2]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.04% [2]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.64% [2]
[1] The fund's investment adviser, The Dreyfus Corporation, has contractually agreed, until March 31, 2018, to waive receipt of its fees and/or assume the direct expenses of Class T shares of the fund so that the expenses of such Class T shares do not exceed .45% (excluding Rule 12b-1 fees, taxes, interest, brokerage commissions, commitment fees on borrowings and extraordinary expenses). On or after March 31, 2018, The Dreyfus Corporation may terminate this expense limitation at any time.
[2] Reflects the performance of the fund's Class A shares, which are offered in a separate prospectus, adjusted to reflect applicable sales charges. Such performance figures have not been adjusted to reflect applicable class fees and expenses.