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Class B Prospectus | General AMT-Free Municipal Money Market Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary - General AMT-Free Municipal Money Market Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks a high level of current income, consistent with stability of principal, that is exempt from federal income taxes.
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 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. 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

To pursue its goal, the fund normally invests substantially all of its assets in short-term, high quality municipal obligations that provide income exempt from federal income taxes. The fund invests at least 80% of its net assets, plus borrowings for investment purposes, in securities exempt from federal income tax and the federal alternative minimum tax. The fund's investments may include municipal notes, short-term municipal bonds, tax-exempt commercial paper and municipal leases. The fund also may invest in high quality, short-term structured notes, which are derivative instruments whose value is tied to underlying municipal obligations.


Although the fund seeks to provide income exempt from federal income taxes, the fund may invest temporarily in high quality, taxable money market instruments, including when the portfolio manager believes acceptable municipal obligations are not available for investment. During such periods, the fund may not achieve its investment objective.


The fund is a money market fund subject to the maturity, quality, liquidity and diversification requirements of Rule 2a-7 under the Investment Company Act of 1940, as amended, and seeks to maintain a stable share price of $1.00.
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. 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's yield will fluctuate as the short-term securities in its portfolio mature or are sold and the proceeds are reinvested in securities with different interest rates. The fund may impose a fee upon the sale of your shares or may temporarily suspend your ability to sell shares (a redemption "gate") if the fund's liquidity falls below required minimums because of market conditions or other factors. Neither The Dreyfus Corporation nor its affiliates have a legal obligation to provide financial support to the fund, and you should not expect that The Dreyfus Corporation or its affiliates will provide financial support to the fund at any time. 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 impair the fund's ability to maintain a stable net asset value. A low interest rate environment may prevent the fund from providing a positive yield or paying fund expenses out of fund assets and could impair the fund's ability to maintain a stable 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 in a timely manner at or near their perceived value. In such a market, the value of such securities may fall dramatically, potentially impairing the fund's ability to maintain a stable net asset value, even during periods of declining 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 a security, can cause the security's price to fall. Although the fund invests only in high quality debt securities, the credit quality of the securities held by the fund can change rapidly in certain market environments, and the default or a significant price decline of a single holding could impair the fund's ability to maintain a stable net asset value.


· Municipal securities risk. Municipal securities may be fully or partially backed or enhanced by the taxing authority of a local government, by the current or anticipated revenues from a specific project or specific assets, or by the credit of, or liquidity enhancement provided by, a private issuer. Special factors, such as legislative changes, and state and local economic and business developments, may adversely affect the yield and/or the fund's ability to maintain a stable net asset value.


· Structured notes risk. Structured notes, a type of derivative instrument, can be volatile, and the possibility of default by the financial institution or counterparty may be greater for these instruments than for other types of money market instruments. Structured notes typically are purchased in privately negotiated transactions from financial institutions and, thus, an active trading market for such instruments may not exist.


· 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 lease risk. Because municipal leases generally are backed by revenues from a particular source or that depend on future appropriations by municipalities and are not obligations of their issuers, they are less secure than most municipal obligations.


· Liquidity fee and/or redemption gate risk. The fund may impose a fee upon the sale of your shares or may temporarily suspend your ability to sell shares (a redemption "gate") if the fund's liquidity falls below required minimums because of unusual market conditions, an unusually high volume of redemption requests, redemptions by a few large investors, or other reasons. If a liquidity fee is imposed by the fund, it would reduce the amount you will receive upon the redemption of your shares. A "gate" will suspend your ability to redeem your shares while the gate is imposed and may prevent the fund from being able to pay redemption proceeds within the allowable time period stated in this prospectus.
Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so.
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 B shares from year to year. The table shows the average annual total returns of the fund's Class B shares over time. The fund's past performance 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.
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 Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dreyfus.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund's past performance 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 (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q1, 2008: 0.59%


Worst Quarter
Q3, 2015: 0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2008
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.59%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn none
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

For the fund’s current yield call toll-free 1-800-DREYFUS (inside the U.S. only).
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns as of 12/31/16
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-800-DREYFUS
Class B Prospectus | General AMT-Free Municipal Money Market Fund | Class B  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.01%
Total annual fund operating expenses rr_ExpensesOverAssets 1.01%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.01%) [1]
Total annual fund operating expenses (after fee waiver and/or expense reimbursement) rr_NetExpensesOverAssets 1.00%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 102
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 318
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 552
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,225
Annual Return 2008 rr_AnnualReturn2008 1.78%
Annual Return 2009 rr_AnnualReturn2009 0.24%
Annual Return 2010 rr_AnnualReturn2010 none
Annual Return 2011 rr_AnnualReturn2011 none
Annual Return 2012 rr_AnnualReturn2012 none
Annual Return 2013 rr_AnnualReturn2013 0.01%
Annual Return 2014 rr_AnnualReturn2014 0.01%
Annual Return 2015 rr_AnnualReturn2015 0.01%
Annual Return 2016 rr_AnnualReturn2016 0.01%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.01%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.01%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 0.36%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jul. 02, 2007
[1] The fund's investment adviser, The Dreyfus Corporation, has agreed in its investment management agreement with the fund to : (1) pay all of the fund's expenses, except management fees, Rule 12b-1 fees and certain other expenses, including the fees and expenses of the non-interested board members and their counsel, and (2) reduce its fees pursuant to the investment management agreement in an amount equal to the fund's allocable portion of the fees and expenses of the non-interested board members and their counsel (in the amount of .01% for the past fiscal year). These provisions in the investment management agreement may not be amended without the approval of the fund's shareholders.