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Institutional Shares Prospectus | Dreyfus Cash Management  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Dreyfus Cash Management
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks as high a level of current income 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, hold and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and examples below.

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)
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Restated to reflect current management fees and shareholder services fees.
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 in a diversified portfolio of high quality, short-term, dollar-denominated debt securities, including: securities issued or guaranteed as to principal and interest by the U.S. government or its agencies or instrumentalities; certificates of deposit, time deposits, bankers' acceptances and other short-term securities issued by domestic or foreign banks or thrifts or their subsidiaries or branches; repurchase agreements, including tri-party repurchase agreements; asset-backed securities; municipal securities; domestic and dollar-denominated foreign commercial paper and other short-term corporate obligations, including those with floating or variable rates of interest; and dollar-denominated obligations issued or guaranteed by one or more foreign governments or any of their political subdivisions or agencies.

The fund's investments are concentrated in the banking industry, because the fund normally invests at least 25% of its net assets in domestic or dollar-denominated foreign bank obligations.

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. Very low or negative interest rates may magnify interest rate risk. In addition, 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. Interest rates in the United States currently are at or near historic lows due to market forces and actions of the Board of Governors of the Federal Reserve System in the U.S., primarily in response to the novel coronavirus (COVID-19) pandemic and resultant market disruptions. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, may result in heightened market volatility and may detract from fund performance. For floating and variable rate obligations, there may be a lag between an actual change in the underlying interest rate benchmark and the reset time for an interest payment of such an obligation, which could harm or benefit the fund, depending on the interest rate environment or other circumstances.

● 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.

● Banking industry risk. The risks generally associated with concentrating investments (i.e., hold 25% or more of its total assets) in the banking industry include interest rate risk, credit risk, and regulatory developments relating to the banking industry. Banks may be particularly susceptible to certain economic factors such as interest rate changes, adverse developments in the real estate market, fiscal and monetary policy and general economic cycles. An adverse development in the banking industry (domestic or foreign) may affect the value of the fund's investments more than if such investments were not concentrated in the banking industry.

● Foreign investment risk. The risks generally associated with dollar-denominated foreign investments include economic and political developments, seizure or nationalization of deposits, imposition of taxes or other restrictions on payment of principal and interest. The imposition of sanctions, confiscations, trade restrictions (including tariffs) and other government restrictions by the United States and other governments, or from problems in share registration, settlement or custody, may also result in losses. In addition, the fund will be subject to the risk that an issuer of foreign sovereign debt or the government authorities that control the repayment of the debt may be unable or unwilling to repay the principal or interest when due.

● U.S. Treasury securities risk. A security backed by the U.S. Treasury or the full faith and credit of the United States is guaranteed only as to the timely payment of interest and principal when held to maturity, but the market prices for such securities are not guaranteed and will fluctuate.

● Government securities risk. Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the fund does not apply to the market value of such security or to shares of the fund itself.

● Repurchase agreement counterparty risk. The fund is subject to the risk that a counterparty in a repurchase agreement and/or, for a tri-party repurchase agreement, the third party bank providing payment administration, collateral custody and management services for the transaction, could fail to honor the terms of the agreement.

● Asset-backed securities risk. Asset-backed securities are subject to credit, prepayment and extension risk, and may be more volatile, less liquid and more difficult to price accurately than more traditional debt securities. General downturns in the economy could cause the value of asset-backed securities to fall. Asset-backed securities are often subject to more rapid repayment than their stated maturity date would indicate as a result of the pass-through of prepayments of principal on the underlying loans. During periods of declining interest rates, prepayment of loans underlying asset-backed securities can be expected to accelerate. Accordingly, the fund's ability to maintain positions in such securities will be affected by reductions in the principal amount of such securities resulting from prepayments, and its ability to reinvest the returns of principal at comparable yields is subject to generally prevailing interest rates at that time.

● 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. In addition, the cost associated with combating the outbreak of COVID-19 and its negative impact on tax revenues has adversely affected the financial condition of many state and local governments. The effects of this outbreak could affect the ability of state and local governments to make payments on debt obligations when due and could adversely impact the value of their bonds.

● Market risk. The value of the securities in which the fund invests may be affected by political, regulatory, economic and social developments, and developments that impact specific economic sectors, industries or segments of the market.  In addition, turbulence in financial markets and reduced liquidity in equity, credit and/or fixed income markets may negatively affect many issuers, which could adversely affect the fund.  Global economies and financial markets are becoming increasingly interconnected, and conditions and events in one country, region or financial market may adversely impact issuers in a different country, region or financial market.  These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies world-wide.  Recent examples include pandemic risks related to COVID-19 and aggressive measures taken world-wide in response by governments, including closing borders, restricting international and domestic travel, and the imposition of prolonged quarantines of large populations, and by businesses, including changes to operations and reducing staff. 

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 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.
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 Institutional shares from year to year. The table shows the average annual total returns of the fund's Institutional 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 (%) Institutional Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q1, 2019: 0.65%

Worst Quarter
Q1, 2015: 0.01%

The year-to-date total return of the fund's Institutional shares as of March 31, 2021 was 0.02%.
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2021
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.65%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.01%
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

For the current yield for Institutional 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 12/31/20
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-800-346-3621
Institutional Shares Prospectus | Dreyfus Cash Management | Institutional Shares  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.10%
Shareholder services fees rr_Component1OtherExpensesOverAssets 0.10%
Miscellaneous other expenses rr_Component3OtherExpensesOverAssets 0.01%
Total other expenses rr_OtherExpensesOverAssets 0.11%
Total annual fund operating expenses rr_ExpensesOverAssets 0.21% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 22
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 68
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 118
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 268
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 22
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 68
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 118
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 268
Annual Return 2011 rr_AnnualReturn2011 0.08%
Annual Return 2012 rr_AnnualReturn2012 0.09%
Annual Return 2013 rr_AnnualReturn2013 0.04%
Annual Return 2014 rr_AnnualReturn2014 0.03%
Annual Return 2015 rr_AnnualReturn2015 0.05%
Annual Return 2016 rr_AnnualReturn2016 0.34%
Annual Return 2017 rr_AnnualReturn2017 1.05%
Annual Return 2018 rr_AnnualReturn2018 2.05%
Annual Return 2019 rr_AnnualReturn2019 2.33%
Annual Return 2020 rr_AnnualReturn2020 0.62%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.62%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.27%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 0.66%
[1] Restated to reflect current management fees and shareholder services fees.