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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName PUTNAM MONEY MARKET FUND
Prospectus Date rr_ProspectusDate Jan. 30, 2014
PUTNAM TAX EXEMPT MONEY MARKET FUND | PUTNAM TAX EXEMPT MONEY MARKET FUND
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading PUTNAM TAX EXEMPT MONEY MARKET
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam Tax Exempt Money Market Fund seeks as high a rate of current income, exempt from federal income tax, as Putnam Investment Management, LLC believes is consistent with preservation of capital and maintenance of liquidity.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 30, 2015
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund's operating expenses remain the same. Only the first year of each period in the example takes into account the expense reimbursement described above. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in money market instruments that pay interest that is exempt from federal income tax but may be subject to the federal alternative minimum tax (AMT), are high quality and have short-term maturities. We may consider, among other factors, credit and interest rate risks, as well as general market conditions when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock The effects of inflation may erode the value of your investment over time. Although the fund seeks to preserve the value of your investment at $1.00 per share, deterioration in the credit quality of issuers whose securities the fund holds or an increase in interest rates may impair the value of your investment, and it is possible to lose money by investing in the fund.

The values of money market investments usually rise and fall in response to changes in interest rates. Interest rate risk is generally lowest for investments with short maturities (a significant part of the fund's investments). Although the fund only buys high quality investments, investments backed by a letter of credit have the risk that the provider of the letter of credit will not be able to fulfill its obligations to the issuer. The amount of information about issuers of tax exempt debt may not be as extensive as that which is available about companies whose securities are publicly traded. Interest the fund receives might be taxable.

The fund may not achieve its goal, and it is not intended to be a complete investment program. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney it is possible to lose money by investing in the fund.
Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the fund seeks to preserve the value of your investment at $1.00 per share, deterioration in the credit quality of issuers whose securities the fund holds or an increase in interest rates may impair the value of your investment, and it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund's performance year to year and over time. Please remember that past performance is not necessarily an indication of future results. Monthly performance figures for the fund are available at putnam.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund's performance year to year and over time.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress putnam.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class A shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best calendar
quarter
Q2 2007		 0.81%
Worst calendar
quarter
Q4 2013		 0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2007
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.81%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
Performance Table Heading rr_PerformanceTableHeading Average annual total returns (for periods ending 12/31/13)
PUTNAM TAX EXEMPT MONEY MARKET FUND | PUTNAM TAX EXEMPT MONEY MARKET FUND | Class A
  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) (mm) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (mm) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management fees rr_ManagementFeesOverAssets 0.29%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.32%
Total annual fund operating expenses rr_ExpensesOverAssets 0.61%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.54%
1 year rr_ExpenseExampleYear01 $ 55
3 years rr_ExpenseExampleYear03 188
5 years rr_ExpenseExampleYear05 333
10 years rr_ExpenseExampleYear10 755
1 year rr_ExpenseExampleNoRedemptionYear01 55
3 years rr_ExpenseExampleNoRedemptionYear03 188
5 years rr_ExpenseExampleNoRedemptionYear05 333
10 years rr_ExpenseExampleNoRedemptionYear10 $ 755
2004 rr_AnnualReturn2004 0.59%
2005 rr_AnnualReturn2005 1.86%
2006 rr_AnnualReturn2006 2.92%
2007 rr_AnnualReturn2007 3.14%
2008 rr_AnnualReturn2008 1.74%
2009 rr_AnnualReturn2009 0.07%
2010 rr_AnnualReturn2010 0.04%
2011 rr_AnnualReturn2011 0.01%
2012 rr_AnnualReturn2012 0.01%
2013 rr_AnnualReturn2013 0.01%
1 year rr_AverageAnnualReturnYear01 0.01%
5 years rr_AverageAnnualReturnYear05 0.03%
10 years rr_AverageAnnualReturnYear10 1.03%
PUTNAM TAX EXEMPT MONEY MARKET FUND | PUTNAM TAX EXEMPT MONEY MARKET FUND | Lipper Tax Exempt Money Market Funds Average (no deduction for taxes)
  
Risk/Return: rr_RiskReturnAbstract  
1 year rr_AverageAnnualReturnYear01 0.02%
5 years rr_AverageAnnualReturnYear05 0.05%
10 years rr_AverageAnnualReturnYear10 1.04%
[1] A deferred sales charge on class A shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund.
[2] Reflects Putnam Investment Management, LLC's contractual obligation to limit certain fund expenses through January 30, 2015. This obligation may be modified or discontinued only with approval of the Board of Trustees.