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Label Element Value
Risk Return Abstract rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Sep. 30, 2015
Registrant Name dei_EntityRegistrantName PUTNAM MONEY MARKET FUND
Central Index Key dei_EntityCentralIndexKey 0000081248
Amendment Flag dei_AmendmentFlag false
Trading Symbol dei_TradingSymbol PDDXK
Document Creation Date dei_DocumentCreationDate Jan. 28, 2016
Document Effective Date dei_DocumentEffectiveDate Jan. 30, 2016
Prospectus Date rr_ProspectusDate Jan. 30, 2016
Putnam Money Market Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summaries
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam Money Market Fund seeks as high a rate of current income 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)
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. 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 are high quality and have short-term maturities. We invest significantly in certificates of deposit, commercial paper (including asset-backed commercial paper), U.S. government debt and repurchase agreements, corporate obligations and bankers acceptances. We may also invest in U.S. dollar denominated foreign securities of these types. 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 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 before sales charges
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Best calendar quarter
Q3 2007   1.26%

Worst calendar quarter
Q4 2015     0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2007
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.26%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn none
Performance Table Heading rr_PerformanceTableHeading Average annual total returns (for periods ending 12/31/15)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Class B share performance reflects conversion to class A shares after eight years.
Putnam Money Market Fund | Class A  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management fees rr_ManagementFeesOverAssets 0.28%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.49%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
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
Annual Return 2006 rr_AnnualReturn2006 4.71%
Annual Return 2007 rr_AnnualReturn2007 4.97%
Annual Return 2008 rr_AnnualReturn2008 2.71%
Annual Return 2009 rr_AnnualReturn2009 0.29%
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 0.01%
Annual Return 2014 rr_AnnualReturn2014 0.01%
Annual Return 2015 rr_AnnualReturn2015 0.01%
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 1.26%
Putnam Money Market Fund | Class B  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 5.00% [1]
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.99%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 601 [1]
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 615 [1]
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 747 [1]
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,071 [1]
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 101
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 315
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 547
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,071
1 Year rr_AverageAnnualReturnYear01 (4.99%)
5 Years rr_AverageAnnualReturnYear05 (0.39%)
10 Years rr_AverageAnnualReturnYear10 1.09%
Putnam Money Market Fund | Class C  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.99%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 315
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 547
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,213
1 Year rr_AverageAnnualReturnYear01 (0.99%)
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 1.09%
Putnam Money Market Fund | Class M  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.15%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.64%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 798
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 1.21%
Putnam Money Market Fund | Class R  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 315
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 547
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,213
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 1.09%
Putnam Money Market Fund | Class T  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none [1]
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.74%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 76
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 237
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 411
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 918
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 1.17%
Putnam Tax Exempt Money Market Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Putnam Tax Exempt Money Market Fund
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, 2017
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. 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. Under normal circumstances, we invest at least 80% of the fund’s net assets in short-term tax-exempt investments, which for purposes of this policy exclude investments paying interest subject to the federal AMT for individuals. This investment policy cannot be changed without the approval of the fund’s shareholders. 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 before sales charges
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Best calendar quarter
Q2 2007  0.81%

Worst calendar quarter
Q4 2015     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, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn none
Performance Table Heading rr_PerformanceTableHeading Average annual total returns (for periods ending 12/31/15)
Putnam Tax Exempt Money Market Fund | Class A  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 1.00% [2]
Management fees rr_ManagementFeesOverAssets 0.28%
Other expenses rr_OtherExpensesOverAssets 0.35%
Total annual fund operating expenses rr_ExpensesOverAssets 0.63%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.09%) [3]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.54%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge on class A shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 55
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 193
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 342
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 778
Annual Return 2006 rr_AnnualReturn2006 2.93%
Annual Return 2007 rr_AnnualReturn2007 3.14%
Annual Return 2008 rr_AnnualReturn2008 1.74%
Annual Return 2009 rr_AnnualReturn2009 0.07%
Annual Return 2010 rr_AnnualReturn2010 0.04%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.01%
Annual Return 2013 rr_AnnualReturn2013 0.01%
Annual Return 2014 rr_AnnualReturn2014 0.01%
Annual Return 2015 rr_AnnualReturn2015 0.01%
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.01%
10 Years rr_AverageAnnualReturnYear10 0.79%
[1] A deferred sales charge on class A, B, C, and T shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.
[2] A deferred sales charge on class A shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund.
[3] Reflects Putnam Investment Management, LLC's contractual obligation to limit certain fund expenses through January 30, 2017. This obligation may be modified or discontinued only with approval of the Board of Trustees.