Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Feb. 28, 2017
Registrant Name	dei_EntityRegistrantName	PUTNAM MONEY MARKET FUND
Central Index Key	dei_EntityCentralIndexKey	0000081248
Amendment Flag	dei_AmendmentFlag	false
Trading Symbol	dei_TradingSymbol	PDDXX
Document Creation Date	dei_DocumentCreationDate	Mar. 10, 2017
Document Effective Date	dei_DocumentEffectiveDate	Apr. 01, 2017
Prospectus Date	rr_ProspectusDate	Jan. 30, 2017
Putnam Money Market Fund
Risk/Return:	rr_RiskReturnAbstract
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. Information about sales charge discounts is available from your financial advisor and in the Appendix to the fund’s prospectus.
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.
Putnam Money Market Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class B
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 552	[2]
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	464	[2]
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	485	[2]
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	640	[2]
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	52
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	164
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	285
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 640
Putnam Money Market Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class M
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class R
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class T
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640

[1] Restated to reflect current fees resulting from a change to the fund's investor servicing arrangements effective September 1, 2016.

[2] Reflects assessment of deferred sales charge assuming Class B shares were acquired by exchange from one or more other Putnam funds immediately after purchase of shares from such other fund(s).