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Administrative Shares Prospectus | Dreyfus Cash Management  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary - 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 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 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 foreign government obligations issued or guaranteed by one or more foreign governments or any of their political subdivisions or agencies.


Normally, the fund invests at least 25% of its 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 (NAV) of the fund's shares will "float," meaning the NAV 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 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 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, 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 have the potential to cause significant deterioration of the fund's NAV.


· Floating NAV risk. The fund does not maintain a stable NAV per share. The NAV of the fund's shares will be calculated to four decimal places and will "float," meaning the NAV 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 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 in the banking industry include interest rate risk, credit risk, and regulatory developments relating to 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.


· 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. 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.


· 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.


· 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.


· 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.

Risk Money Market Fund [Text] rr_RiskMoneyMarketFund 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 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 Administrative shares from year to year. The table shows the average annual total returns of the fund's Administrative 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
Q3, 2007: 1.29%

Worst Quarter
Q3, 2015: 0.00%

The year-to-date total return of the fund's Administrative shares as of March 31, 2017 was 0.16%.
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2017
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.16%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2007
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.29%
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 Administrative shares call toll-free 1-800-346-3621. Individuals or entities for whom institutions may purchase or redeem shares should call the institution directly.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns as of 12/31/16
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-800-346-3621
Administrative Shares Prospectus | Dreyfus Cash Management | administrative shares  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.20%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.10%
Other expenses rr_OtherExpensesOverAssets 0.02%
Total annual fund operating expenses rr_ExpensesOverAssets 0.32%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 33
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 103
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 180
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 406
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 33
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 103
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 180
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 406
Annual Return 2007 rr_AnnualReturn2007 5.14%
Annual Return 2008 rr_AnnualReturn2008 2.83%
Annual Return 2009 rr_AnnualReturn2009 0.43%
Annual Return 2010 rr_AnnualReturn2010 0.05%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.01%
Annual Return 2013 rr_AnnualReturn2013 none
Annual Return 2014 rr_AnnualReturn2014 none
Annual Return 2015 rr_AnnualReturn2015 0.01%
Annual Return 2016 rr_AnnualReturn2016 0.24%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.24%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.05%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 0.86%