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Investor Shares | Dreyfus Amt-Free Tax Exempt Cash Management Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary - Dreyfus Amt-Free Tax Exempt Cash Management 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 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 also may invest in high quality, short-term structured notes, which are derivative instruments whose value is tied to underlying municipal obligations. In addition, the fund may invest temporarily in high quality, taxable money market instruments, including when the portfolio manager believes that acceptable municipal obligations are unavailable for investment.


Although the fund is permitted to invest up to 20% of its assets in municipal obligations that provide income that may be subject to the federal alternative minimum tax, the fund currently is managed so that income paid by the fund will not be subject to the federal alternative minimum tax.


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, although the net asset value of the fund's shares will "float," meaning the net asset value will fluctuate with changes in the values of the fund's portfolio securities.
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.  Because the share price of the fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them.  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 shares (a "liquidity fee") 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 BNY Mellon Investment Adviser, Inc. nor its affiliates have a legal obligation to provide financial support to the fund, and you should not expect that BNY Mellon Investment Adviser, Inc. 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 cause the fund's share price to decline. A low interest rate environment may prevent the fund from providing a positive yield or paying fund expenses out of fund assets and could lead to a decline in the fund's share price.


● 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 leading to a decline in the fund's share price.


● 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. 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 have the potential to cause significant deterioration of the fund's net asset value.


● Floating net asset value risk. The fund does not maintain a stable net asset value per share. The net asset value of the fund's shares will be calculated to four decimal places and will "float," meaning the net asset value will fluctuate with changes in the values of the fund's portfolio securities. You could lose money by investing in the fund.


● Liquidity fee and/or redemption gate risk. The fund may impose a fee upon the sale of your shares (a "liquidity fee") 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.


● 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 value of the fund's investments in municipal securities.


● 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.


● Market risk. The value of the securities in which the fund invests may be affected by political, regulatory, economic and social developments.  Events such as war, acts of terrorism, the spread of infectious illness or other public health issue, recessions, or other events could have a significant impact on the fund and its investments.
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in the 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.
Risk Money Market Fund May Impose Fees or Suspend Sales [Text] rr_RiskMoneyMarketFundMayImposeFeesOrSuspendSales The fund may impose a fee upon the sale of shares (a "liquidity fee") 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.
Risk Money Market Fund Price Fluctuates [Text] rr_RiskMoneyMarketFundPriceFluctuates Because the share price of the fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them.
Risk Money Market Fund Sponsor May Not Provide Support [Text] rr_RiskMoneyMarketFundSponsorMayNotProvideSupport Neither BNY Mellon Investment Adviser, Inc. nor its affiliates have a legal obligation to provide financial support to the fund, and you should not expect that BNY Mellon Investment Adviser, Inc. or its affiliates will provide financial support to the fund at any time.
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 Investor shares from year to year. The table shows the average annual total returns of the fund's Investor 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 (%) Investor Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q2, 2019: 0.32%

Worst Quarter
Q3, 2015: 0.00%


The year-to-date total return of the fund's Investor shares as of March 31, 2020 was 0.24%.
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2020
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.24%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.32%
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 current yield for Investor shares call toll-free 1-800-346-3621. Individuals or entities for whom institutions may purchase or redeem shares should call the institution directly.
Average Annual Return, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns as of 12/31/19
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-800-346-3621
Investor Shares | Dreyfus Amt-Free Tax Exempt Cash Management Fund | DREYFUS AMT-FREE TAX EXEMPT CASH MANAGEMENT - Investor Shares  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.20%
Other expenses: Shareholder services fees rr_Component1OtherExpensesOverAssets 0.25%
Other expenses: Miscellaneous other expenses rr_Component3OtherExpensesOverAssets 0.04%
Total other expenses rr_OtherExpensesOverAssets 0.29%
Total annual fund operating expenses rr_ExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 157
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 274
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 616
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 50
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 157
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 274
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 616
Annual Return 2010 rr_AnnualReturn2010 0.01%
Annual Return 2011 rr_AnnualReturn2011 none
Annual Return 2012 rr_AnnualReturn2012 none
Annual Return 2013 rr_AnnualReturn2013 none
Annual Return 2014 rr_AnnualReturn2014 0.01%
Annual Return 2015 rr_AnnualReturn2015 0.01%
Annual Return 2016 rr_AnnualReturn2016 0.07%
Annual Return 2017 rr_AnnualReturn2017 0.36%
Annual Return 2018 rr_AnnualReturn2018 1.00%
Annual Return 2019 rr_AnnualReturn2019 1.07%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 1.07%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.50%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 0.25%