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Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary - BNY Mellon National Municipal Money Market Fund
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 and the maintenance of liquidity.

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.

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)
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 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Strategy [Heading] rr_StrategyHeading Principal Investment Strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

As a money market fund, the fund is subject to the maturity, quality, liquidity and diversification requirements of Rule 2a-7 under the Investment Company Act of 1940, as amended, which are designed to help money market funds maintain a stable share price of $1.00.


To pursue its goal, the fund invests at least 80% of its net assets in short-term, high quality municipal obligations that provide income exempt from federal income tax. Among these are municipal notes, short-term municipal bonds, tax-exempt commercial paper and municipal leases.


Although the fund seeks to provide income exempt from federal income tax, income from some of the fund's holdings may be subject to the federal alternative minimum tax.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.


The fund's yield will fluctuate as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. Additionally, while the fund has maintained a constant share price since inception, and will continue to try to do so, neither the investment adviser nor its affiliates are required to make a capital infusion, enter into a capital support agreement or take other actions to prevent the fund's share price from falling below $1.00. The following are the principal risks that could reduce the fund's income level and/or share price:


· Interest rate risk. This risk refers to the decline in the prices of fixed-income securities that may accompany a rise in the overall level of interest rates. A sharp and unexpected rise in interest rates could cause a money market fund's share price to drop below a dollar.


· Credit risk. Failure of an issuer to make timely interest or principal payments, or a decline or perception of a decline in the credit quality of a security, can cause the security's price to fall, potentially lowering the fund's share price. Although the fund invests only in high quality debt securities, any of the fund's holdings could have its credit rating downgraded or could default. The credit quality of the securities held by the fund can change rapidly in certain market environments, and the default of a single holding could have the potential to cause significant deterioration of the fund's net asset value.


· 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 at or near their perceived value. In such a market, the value of such securities may fall dramatically, potentially lowering the fund's share price, even during periods of declining interest rates. Also, during such periods, redemptions by a few large investors in the fund may have a significant adverse effect on the fund's net asset value and remaining fund shareholders.


· Tax risk. To be tax-exempt, municipal obligations generally must meet certain regulatory requirements. If any such municipal obligation fails to meet these regulatory requirements, the interest received by the fund from its investment in such obligations and distributed to fund shareholders will be taxable.


· 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.

Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund 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 M shares from year to year. The table shows the average annual total returns of the fund's Class M shares and Investor shares over time. The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. Performance for each share class will vary due to differences in 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 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 M
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q2, 2007: 0.87%
 Worst Quarter
Q4, 2012: 0.00%


The year-to-date total return of the fund’s Class M shares as of September 30, 2013 was 0.00%.

Year to Date Return, Label rr_YearToDateReturnLabel The year-to-date total return of the fund's Class M shares
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2007
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.87%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2012
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

For the fund's current yield, Wealth Management Clients may call toll free 1-888-281-7350; Individual Clients may call toll free 1-800-DREYFUS (inside the U.S. only); BNY Mellon Wealth Brokerage Clients may call toll free 1-800-830-0549 — Option 2 for BNY Mellon Wealth Management Direct or Option 3 for BNY Mellon Wealth Advisors; participants in Qualified Employee Benefit Plans may call toll free 1-877-774-0327; and Institutional Investors and clients of Investment Advisory Firms may call toll free 1-888-281-7350.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns as of 12/31/12
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-888-281-7350
Class M Shares
  
Risk/Return: rr_RiskReturnAbstract  
Investment advisory fees rr_ManagementFeesOverAssets 0.15%
Other expenses - Shareholder services fees rr_Component1OtherExpensesOverAssets none
Other expenses - Administration fees rr_Component2OtherExpensesOverAssets 0.12%
Other expenses - Other expenses of the fund rr_Component3OtherExpensesOverAssets 0.03%
Total annual fund operating expenses rr_ExpensesOverAssets 0.30%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 31
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 97
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 169
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 381
Annual Return 2004 rr_AnnualReturn2004 0.89%
Annual Return 2005 rr_AnnualReturn2005 2.10%
Annual Return 2006 rr_AnnualReturn2006 3.16%
Annual Return 2007 rr_AnnualReturn2007 3.39%
Annual Return 2008 rr_AnnualReturn2008 1.93%
Annual Return 2009 rr_AnnualReturn2009 0.16%
Annual Return 2010 rr_AnnualReturn2010 0.06%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.00%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 none
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.43%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.25%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jun. 02, 2003
Investor Shares
  
Risk/Return: rr_RiskReturnAbstract  
Investment advisory fees rr_ManagementFeesOverAssets 0.15%
Other expenses - Shareholder services fees rr_Component1OtherExpensesOverAssets 0.25%
Other expenses - Administration fees rr_Component2OtherExpensesOverAssets 0.12%
Other expenses - Other expenses of the fund rr_Component3OtherExpensesOverAssets 0.05%
Total annual fund operating expenses rr_ExpensesOverAssets 0.57%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 58
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 183
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 318
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 714
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 none
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.34%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.09%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jun. 02, 2003