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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MORGAN STANLEY US GOVERNMENT MONEY MARKET TRUST
Objective [Heading] rr_ObjectiveHeading Investment Objectives
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Morgan Stanley U.S. Government Money Market Trust (the "Fund") is a money market fund that seeks to provide security of principal, high current income and liquidity.

Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. The Fund is a no-load fund. The Fund does not impose any sales charges and does not impose account or exchange fees.

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 below 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, your investment has a 5% return each year, and 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 Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests in high quality, short-term U.S. government securities. In selecting investments, the Adviser seeks to maintain the Fund's share price at $1.00.


The U.S. government securities that the Fund may purchase include U.S. Treasury bills, notes and bonds, all of which are direct obligations of the U.S. Government. In addition, the Fund may purchase securities issued by agencies and instrumentalities of the U.S. Government which are backed by the full faith and credit of the United States. Among the agencies and instrumentalities issuing these obligations are the Government National Mortgage Association ("Ginnie Mae") and the Federal Housing Administration. The Fund may also purchase securities issued by agencies and instrumentalities which are not backed by the full faith and credit of the United States, but whose issuing agency or instrumentality has the right to borrow, to meet its obligations, from the U.S. Treasury. Among these agencies and instrumentalities are the Federal National Mortgage Association ("Fannie Mae"), the Federal Home Loan Mortgage Corporation ("Freddie Mac") and the Federal Home Loan Banks. Further, the Fund may purchase securities issued by agencies and instrumentalities which are backed solely by the credit of the issuing agency or instrumentality. Among these agencies and instrumentalities is the Federal Farm Credit System. The Fund may also invest in repurchase agreements.

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

There is no assurance that the Fund will achieve its investment objectives. Although the Fund seeks to preserve the value of your investment at $1.00 per share, if it is unable to do so, it is possible to lose money by investing in the Fund. The principal risks of investing in this Fund include:


•  U.S. Government Securities. The U.S. government securities in which the Fund invests can be subject to two types of risk: credit risk and interest rate risk. When the general level of interest rates goes up, the prices of most fixed-income securities go down. When the general level of interest rates goes down, the prices of most fixed-income securities go up. With respect to U.S. government securities that are not backed by the full faith and credit of the United States, there is the risk that the U.S. Government will not provide financial support to such U.S. government agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law.


•  Repurchase Agreements. Repurchase agreements are subject to risks associated with the possibility of default by the seller at a time when the collateral has declined in value, or insolvency of the seller, which may affect the Fund's right to control the collateral and result in certain costs and delays. Repurchase agreements may involve a greater degree of credit risk than investments in U.S. government securities.


Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency.

Risk Lose Money [Text] rr_RiskLoseMoney Although the Fund seeks to preserve the value of your investment at $1.00 per share, if it is unable to do so, it is possible to lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing the Fund's average annual returns for the one, five and 10 year periods. The Fund's past performance does not indicate how the Fund will perform in the future.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing the Fund's average annual returns for the one, five and 10 year periods.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance does not indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns-Calendar Years
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

The year-to-date total return as of March 31, 2013 was 0.00%.


High Quarter

 

9/30/06

   

1.16

%

 

Low Quarter

 

3/31/10

   

0.00

%

 
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel High Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2006
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.16%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Low Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

For the Fund's most recent 7-day annualized yield, you may call toll-free (800) 869-NEWS.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For Periods Ended December 31, 2012
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone (800) 869-NEWS
MORGAN STANLEY US GOVERNMENT MONEY MARKET TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Advisory Fee rr_ManagementFeesOverAssets 0.35%
Shareholder Servicing Fees rr_Component1OtherExpensesOverAssets 0.10%
Other Expenses rr_OtherExpensesOverAssets 0.10%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.55% [1]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.39%) [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursements rr_NetExpensesOverAssets 0.16% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 16
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 52
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 90
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 205
Annual Return 2003 rr_AnnualReturn2003 0.47%
Annual Return 2004 rr_AnnualReturn2004 0.68%
Annual Return 2005 rr_AnnualReturn2005 2.52%
Annual Return 2006 rr_AnnualReturn2006 4.39%
Annual Return 2007 rr_AnnualReturn2007 4.60%
Annual Return 2008 rr_AnnualReturn2008 1.86%
Annual Return 2009 rr_AnnualReturn2009 0.02%
Annual Return 2010 rr_AnnualReturn2010 0.01%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.01%
Average Annual Returns, Past 1 Year rr_AverageAnnualReturnYear01 0.01%
Average Annual Returns, Past 5 Years rr_AverageAnnualReturnYear05 0.38%
Average Annual Returns, Past 10 Years rr_AverageAnnualReturnYear10 1.44%
[1] The Fund's "Distributor," Morgan Stanley Distribution, Inc., its "Adviser," Morgan Stanley Investment Management Inc. and its "Administrator," Morgan Stanley Services Company Inc. have agreed to waive and/or reimburse all or a portion of the Fund's distribution fee, advisory fee and administration fee, respectively, to the extent that total expenses exceed total income on a daily basis. These fee waivers and/or expense reimbursements will continue for at least one year or until such time as the Fund's Board of Trustees acts to discontinue all or a portion of such waivers and/or reimbursements when it deems such action is appropriate.