Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2016
Registrant Name	dei_EntityRegistrantName	PUTNAM MULTI-CAP GROWTH FUND
Central Index Key	dei_EntityCentralIndexKey	0000865177
Amendment Flag	dei_AmendmentFlag	false
Trading Symbol	dei_TradingSymbol	PNOPX
Document Creation Date	dei_DocumentCreationDate	Oct. 30, 2017
Document Effective Date	dei_DocumentEffectiveDate	Oct. 30, 2017
Prospectus Date	rr_ProspectusDate	Oct. 30, 2017
Putnam Multi-Cap Growth Fund
Risk Return Abstract	rr_RiskReturnAbstract
Objective [Heading]	rr_ObjectiveHeading	Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Putnam Multi-Cap Growth Fund seeks long-term capital appreciation.
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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds. More information about these and other discounts is available from your financial advisor and in How do I buy fund shares? beginning on page 12 of the fund’s prospectus, in the Appendix to the fund’s prospectus, and in How to buy shares beginning on page II-1 of the fund’s statement of additional information (SAI).
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)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs and may result in higher taxes when the fund’s shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 76%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	76.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds. More information about these and other discounts is available from your financial advisor and in How do I buy fund shares? beginning on page 12 of the fund’s prospectus, in the Appendix to the fund’s prospectus, and in How to buy shares beginning on page II-1 of the fund’s statement of additional information (SAI).
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
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, except as indicated, redeem 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, risks, and performance Investments
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	We invest mainly in common stocks of U.S. companies of any size, with a focus on growth stocks. Growth stocks are issued by companies whose earnings are expected to grow faster than those of similar firms, and whose business growth and other characteristics may lead to an increase in stock price. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading]	rr_RiskHeading	Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	It is important to understand that you can lose money by investing in the fund. The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and the market may not favor growth-style investing. These risks are generally greater for small and midsize companies. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which would make the fund more vulnerable to adverse developments affecting those industries or sectors. 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 important to understand that you can 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. The bar chart does not reflect the impact of sales charges. If it did, performance would be lower. 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 Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart does not reflect the impact of sales charges. If it did, performance would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Year-to-date performance through 9/30/17    21.71% Best calendar quarter Q1 2012    17.95% Worst calendar quarter Q4 2008    –22.04%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-date performance through
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2017
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	21.71%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best calendar quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	17.95%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst calendar quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(22.04%)
Performance Table Heading	rr_PerformanceTableHeading	Average annual total returns after sales charges (for periods ending 12/31/16)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns reflect the historical highest individual federal marginal income tax rates and do not reflect state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on an investor’s tax situation and may differ from those shown.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for class A shares only and will vary for other classes.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	After-tax returns reflect the historical highest individual federal marginal income tax rates and do not reflect state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are shown for class A shares only and will vary for other classes. These after-tax returns do not apply if you hold your fund shares through a 401(k) plan, an IRA, or another tax-advantaged arrangement. Class B share performance reflects conversion to class A shares after eight years.
Putnam Multi-Cap Growth Fund | Class A
Risk Return Abstract	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
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	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.00%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 671
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	875
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,096
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,729
Annual Return 2007	rr_AnnualReturn2007	5.64%
Annual Return 2008	rr_AnnualReturn2008	(38.53%)
Annual Return 2009	rr_AnnualReturn2009	31.82%
Annual Return 2010	rr_AnnualReturn2010	19.31%
Annual Return 2011	rr_AnnualReturn2011	(5.00%)
Annual Return 2012	rr_AnnualReturn2012	16.70%
Annual Return 2013	rr_AnnualReturn2013	36.28%
Annual Return 2014	rr_AnnualReturn2014	13.35%
Annual Return 2015	rr_AnnualReturn2015	(0.40%)
Annual Return 2016	rr_AnnualReturn2016	7.65%
1 Year	rr_AverageAnnualReturnYear01	1.46%
5 Years	rr_AverageAnnualReturnYear05	12.74%
10 Years	rr_AverageAnnualReturnYear10	5.86%
Putnam Multi-Cap Growth 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%	[4]
Management fees	rr_ManagementFeesOverAssets	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.75%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 678
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	851
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,149
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,864
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	178
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	551
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	949
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,864
1 Year	rr_AverageAnnualReturnYear01	1.85%
5 Years	rr_AverageAnnualReturnYear05	12.99%
10 Years	rr_AverageAnnualReturnYear10	5.85%
Putnam Multi-Cap Growth 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%	[5]
Management fees	rr_ManagementFeesOverAssets	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.75%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 278
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	551
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	949
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,062
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	178
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	551
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	949
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,062
1 Year	rr_AverageAnnualReturnYear01	5.83%
5 Years	rr_AverageAnnualReturnYear05	13.23%
10 Years	rr_AverageAnnualReturnYear10	5.69%
Putnam Multi-Cap Growth Fund | Class M
Risk Return Abstract	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	3.50%
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	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.50%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 497
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	807
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,140
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 2,078
1 Year	rr_AverageAnnualReturnYear01	3.35%
5 Years	rr_AverageAnnualReturnYear05	12.71%
10 Years	rr_AverageAnnualReturnYear10	5.58%
Putnam Multi-Cap Growth 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	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.25%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 127
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	397
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	686
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,511
1 Year	rr_AverageAnnualReturnYear01	7.38%
5 Years	rr_AverageAnnualReturnYear05	13.80%
10 Years	rr_AverageAnnualReturnYear10	6.22%
Putnam Multi-Cap Growth Fund | Class T
Risk Return Abstract	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	2.50%
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	0.51%	[2]
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.24%	[6]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.00%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 349
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	560
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	789
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,444
1 Year	rr_AverageAnnualReturnYear01	4.96%	[7]
5 Years	rr_AverageAnnualReturnYear05	13.51%	[7]
10 Years	rr_AverageAnnualReturnYear10	6.22%	[7]
Putnam Multi-Cap Growth Fund | Class Y
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	0.51%	[2]
Other expenses	rr_OtherExpensesOverAssets	0.24%	[3]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.75%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 77
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	240
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	417
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 930
1 Year	rr_AverageAnnualReturnYear01	7.91%
5 Years	rr_AverageAnnualReturnYear05	14.37%
10 Years	rr_AverageAnnualReturnYear10	6.76%
Putnam Multi-Cap Growth Fund | after taxes on distributions | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.46%
5 Years	rr_AverageAnnualReturnYear05	11.41%
10 Years	rr_AverageAnnualReturnYear10	5.23%
Putnam Multi-Cap Growth Fund | after taxes on distributions and sale of fund shares | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.82%
5 Years	rr_AverageAnnualReturnYear05	10.05%
10 Years	rr_AverageAnnualReturnYear10	4.64%
Putnam Multi-Cap Growth Fund | Russell 3000 Growth Index (no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	7.39%	[8]
5 Years	rr_AverageAnnualReturnYear05	14.44%	[8]
10 Years	rr_AverageAnnualReturnYear10	8.28%	[8]

[1] Applies only to certain redemptions of shares bought with no initial sales charge.

[2] Management fees reflect a performance adjustment. The fund's base management fee is subject to adjustment, up or down, based on the fund's performance relative to the performance of the Russell 3000 Growth Index. For the most recent fiscal year, the fund's base management fee prior to any performance adjustment was 0.555%.

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

[4] This charge is phased out over six years.

[5] This charge is eliminated after one year.

[6] Other expenses are based on expenses of class A shares for the fund's last fiscal year, as restated to reflect current fees resulting from a change to the fund's investor servicing arrangements effective September 1, 2016.

[7] Class T shares were not outstanding during the periods shown. Performance shown for class T shares is derived from the historical performance of class A shares, adjusted for the lower initial sales charge currently applicable to class T shares.

[8] Frank Russell Company is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell(R) is a trademark of Frank Russell Company