Label	Element	Value
Prospectus [Line Items]	rr_ProspectusLineItems
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2019
Entity Registrant Name	dei_EntityRegistrantName	PUTNAM CONVERTIBLE SECURITIES FUND
Entity Central Index Key	dei_EntityCentralIndexKey	0000081247
Amendment Flag	dei_AmendmentFlag	false
Entity Inv Company Type	dei_EntityInvCompanyType	N-1A
Trading Symbol	dei_TradingSymbol	PCONX
Document Creation Date	dei_DocumentCreationDate	Feb. 27, 2020
Document Effective Date	dei_DocumentEffectiveDate	Feb. 29, 2020
Prospectus Date	rr_ProspectusDate	Feb. 29, 2020
Class A B C R R6 Y | Putnam Convertible Securities Fund
Prospectus [Line Items]	rr_ProspectusLineItems
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary
Objective [Heading]	rr_ObjectiveHeading	Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Putnam Convertible Securities Fund seeks, with equal emphasis, current income and capital appreciation.
Objective, Secondary [Text Block]	rr_ObjectiveSecondaryTextBlock	Its secondary objective is conservation of capital.
Expense [Heading]	rr_ExpenseHeading	Fees and expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following tables describe 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 14 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 60%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	60.00%
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 14 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
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Investments We invest mainly in convertible securities of U.S. companies. Under normal circumstances, we invest at least 80% of the fund’s net assets in convertible securities. This policy may be changed only after 60 days’ notice to shareholders. Convertible securities combine the investment characteristics of bonds and common stocks. Convertible securities include bonds, preferred stocks and other instruments that can be converted into or exchanged for common stock or equivalent value. A significant portion of the convertible securities we buy are below-investment-grade (sometimes referred to as “junk bonds”). The convertible bonds we buy usually have intermediate- to long-term stated maturities (i.e., three years or longer), but often contain “put” features, which allow bondholders to sell the bond back to the company under specified circumstances, that result in shorter effective maturities. When deciding whether to buy or sell investments, we may consider, among other factors: (i) a security’s structural features, such as its position in a company’s capital structure and “put” and “call” features (a company’s right to repurchase the security under specified circumstances is a “call” feature); (ii) credit and prepayment risks; and (iii) with respect to a company’s common stock underlying a convertible security, the stock’s valuation and the company’s financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends.
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 investments in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general economic, political or financial market conditions, investor sentiment and market perceptions, government actions, geopolitical events or changes, and factors related to a specific issuer, asset class, geography, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. These risks are generally greater for convertible securities issued by small and midsize companies (which may constitute a significant portion of the fund’s investments from time to time). The value of convertible securities may be adversely affected by changes in the prices of underlying common stocks. Convertible securities tend to provide higher yields than common stocks. However, a higher yield may not protect investors against the risk of loss or adequately mitigate any loss associated with a decline in the price of a convertible security. Convertible securities are subject to credit risk, which is the risk that an issuer of the fund’s investments may default on payment of interest or principal. Credit risk is generally greater for below-investment-grade convertible securities (a significant part of the fund’s investments). Generally, convertible securities may be less sensitive to interest rate changes than non-convertible bonds as a result of convertible securities’ convertibility and “put” features. Interest rate risk is generally greater for longer-term bonds and convertible securities whose underlying stock price has fallen significantly below the conversion price. There is no guarantee that the investment techniques, analyses, or judgments that we apply in making investment decisions for the fund will produce the intended outcome or that the investments we select for the fund will perform as well as other securities that were not selected for the fund. 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	Best calendar quarter Q1 2019   11.88% Worst calendar quarter Q3 2011 −14.14%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-date performance
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best calendar quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	11.88%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst calendar quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(14.14%)
Performance Table Heading	rr_PerformanceTableHeading	Average annual total returns after sales charges (for periods ended 12/31/19)
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	ICE BofA Indexes: ICE Data Indices, LLC (“ICE BofA”), used with permission. ICE BofA permits use of the ICE BofA indices and related data on an “as is” basis; makes no warranties regarding same; does not guarantee the suitability, quality, accuracy, timeliness, and/or completeness of the ICE BofA indices or any data included in, related to, or derived therefrom; assumes no liability in connection with the use of the foregoing; and does not sponsor, endorse, or recommend Putnam Investments, or any of its products or services. 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.
Class A B C R R6 Y | Putnam Convertible Securities Fund | ICE BofA U.S. Convertible Index (no deduction for fees, expenses or taxes)
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	23.15%
5 Years	rr_AverageAnnualReturnYear05	8.48%
10 Years	rr_AverageAnnualReturnYear10	10.09%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class A
Prospectus [Line Items]	rr_ProspectusLineItems
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	0.62%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.05%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 676
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	890
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,121
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,784
Annual Return 2010	rr_AnnualReturn2010	19.55%
Annual Return 2011	rr_AnnualReturn2011	(6.47%)
Annual Return 2012	rr_AnnualReturn2012	15.09%
Annual Return 2013	rr_AnnualReturn2013	21.96%
Annual Return 2014	rr_AnnualReturn2014	7.47%
Annual Return 2015	rr_AnnualReturn2015	(7.03%)
Annual Return 2016	rr_AnnualReturn2016	9.51%
Annual Return 2017	rr_AnnualReturn2017	14.93%
Annual Return 2018	rr_AnnualReturn2018	(3.26%)
Annual Return 2019	rr_AnnualReturn2019	24.31%
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	17.16%
5 Years	rr_AverageAnnualReturnYear05	5.81%
10 Years	rr_AverageAnnualReturnYear10	8.38%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class A | after taxes on distributions
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	14.68%
5 Years	rr_AverageAnnualReturnYear05	3.92%
10 Years	rr_AverageAnnualReturnYear10	6.86%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class A | after taxes on distributions and sale of fund shares
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	11.14%
5 Years	rr_AverageAnnualReturnYear05	4.01%
10 Years	rr_AverageAnnualReturnYear10	6.31%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class B
Prospectus [Line Items]	rr_ProspectusLineItems
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%	[2]
Management fees	rr_ManagementFeesOverAssets	0.62%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.80%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 683
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	866
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,175
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,919
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	183
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	566
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	975
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,919
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	18.36%
5 Years	rr_AverageAnnualReturnYear05	5.95%
10 Years	rr_AverageAnnualReturnYear10	8.38%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class C
Prospectus [Line Items]	rr_ProspectusLineItems
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%	[3]
Management fees	rr_ManagementFeesOverAssets	0.62%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.80%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 283
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	566
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	975
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,116
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	183
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	566
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	975
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,116
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	22.37%
5 Years	rr_AverageAnnualReturnYear05	6.27%
10 Years	rr_AverageAnnualReturnYear10	8.21%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class R
Prospectus [Line Items]	rr_ProspectusLineItems
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	0.62%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.30%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 132
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	412
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	713
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,568
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	23.97%
5 Years	rr_AverageAnnualReturnYear05	6.81%
10 Years	rr_AverageAnnualReturnYear10	8.75%
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class R6
Prospectus [Line Items]	rr_ProspectusLineItems
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	0.62%
Other expenses	rr_OtherExpensesOverAssets	0.10%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.72%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 74
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	230
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	401
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 894
Label	rr_AverageAnnualReturnLabel	before taxes	[4]
1 Year	rr_AverageAnnualReturnYear01	24.73%	[4]
5 Years	rr_AverageAnnualReturnYear05	7.37%	[4]
10 Years	rr_AverageAnnualReturnYear10	9.31%	[4]
Class A B C R R6 Y | Putnam Convertible Securities Fund | Class Y
Prospectus [Line Items]	rr_ProspectusLineItems
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	0.62%
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.80%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 82
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	255
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	444
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 990
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	24.64%
5 Years	rr_AverageAnnualReturnYear05	7.34%
10 Years	rr_AverageAnnualReturnYear10	9.30%
Class I | Putnam Convertible Securities Fund
Prospectus [Line Items]	rr_ProspectusLineItems
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary
Objective [Heading]	rr_ObjectiveHeading	Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Putnam Convertible Securities Fund seeks, with equal emphasis, current income and capital appreciation.
Objective, Secondary [Text Block]	rr_ObjectiveSecondaryTextBlock	Its secondary objective is conservation of capital.
Expense [Heading]	rr_ExpenseHeading	Fees and expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following tables describe the fees and expenses you may pay if you buy and hold Class I 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)
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 60%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	60.00%
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 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
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Investments We invest mainly in convertible securities of U.S. companies. Under normal circumstances, we invest at least 80% of the fund’s net assets in convertible securities. This policy may be changed only after 60 days’ notice to shareholders. Convertible securities combine the investment characteristics of bonds and common stocks. Convertible securities include bonds, preferred stocks and other instruments that can be converted into or exchanged for common stock or equivalent value. A significant portion of the convertible securities we buy are below-investment-grade (sometimes referred to as “junk bonds”). The convertible bonds we buy usually have intermediate- to long-term stated maturities (i.e., three years or longer), but often contain “put” features, which allow bondholders to sell the bond back to the company under specified circumstances, that result in shorter effective maturities. When deciding whether to buy or sell investments, we may consider, among other factors: (i) a security’s structural features, such as its position in a company’s capital structure and “put” and “call” features (a company’s right to repurchase the security under specified circumstances is a “call” feature); (ii) credit and prepayment risks; and (iii) with respect to a company’s common stock underlying a convertible security, the stock’s valuation and the company’s financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends.
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 investments in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general economic, political or financial market conditions, investor sentiment and market perceptions, government actions, geopolitical events or changes, and factors related to a specific issuer, asset class, geography, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. These risks are generally greater for convertible securities issued by small and midsize companies (which may constitute a significant portion of the fund’s investments from time to time). The value of convertible securities may be adversely affected by changes in the prices of underlying common stocks. Convertible securities tend to provide higher yields than common stocks. However, a higher yield may not protect investors against the risk of loss or adequately mitigate any loss associated with a decline in the price of a convertible security. Convertible securities are subject to credit risk, which is the risk that an issuer of the fund’s investments may default on payment of interest or principal. Credit risk is generally greater for below-investment-grade convertible securities (a significant part of the fund’s investments). Generally, convertible securities may be less sensitive to interest rate changes than non-convertible bonds as a result of convertible securities’ convertibility and “put” features. Interest rate risk is generally greater for longer-term bonds and convertible securities whose underlying stock price has fallen significantly below the conversion price. There is no guarantee that the investment techniques, analyses, or judgments that we apply in making investment decisions for the fund will produce the intended outcome or that the investments we select for the fund will perform as well as other securities that were not selected for the fund. 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. Performance for class I shares prior to their inception (3/3/15) is derived from the historical performance of class Y shares, which are not offered in this prospectus, and has not been adjusted for the lower fees applicable to class I shares; had it, returns would have been higher. Please remember that past performance is not necessarily an indication of future results.
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 I shares
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	Best calendar quarter Q1 2019  11.98% Worst calendar quarter Q4 2018 −9.79%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-date performance
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best calendar quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	11.98%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst calendar quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(9.79%)
Performance Table Heading	rr_PerformanceTableHeading	Average annual total returns after sales charges (for periods ended 12/31/19)
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	ICE BofA Indexes: ICE Data Indices, LLC (“ICE BofA”), used with permission. ICE BofA permits use of the ICE BofA indices and related data on an “as is” basis; makes no warranties regarding same; does not guarantee the suitability, quality, accuracy, timeliness, and/or completeness of the ICE BofA indices or any data included in, related to, or derived therefrom; assumes no liability in connection with the use of the foregoing; and does not sponsor, endorse, or recommend Putnam Investments, or any of its products or services. 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.
Class I | Putnam Convertible Securities Fund | ICE BofA U.S. Convertible Index
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	23.15%
5 Years	rr_AverageAnnualReturnYear05	8.48%
10 Years	rr_AverageAnnualReturnYear10	10.09%
Class I | Putnam Convertible Securities Fund | Class I
Prospectus [Line Items]	rr_ProspectusLineItems
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	0.62%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets
Other expenses	rr_OtherExpensesOverAssets	0.06%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.68%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 69
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	218
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	379
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 847
Annual Return 2016	rr_AnnualReturn2016	9.95%
Annual Return 2017	rr_AnnualReturn2017	15.42%
Annual Return 2018	rr_AnnualReturn2018	(2.90%)
Annual Return 2019	rr_AnnualReturn2019	24.74%
Label	rr_AverageAnnualReturnLabel	before taxes
1 Year	rr_AverageAnnualReturnYear01	24.74%
5 Years	rr_AverageAnnualReturnYear05	7.48%
10 Years	rr_AverageAnnualReturnYear10	9.37%
Class I | Putnam Convertible Securities Fund | Class I | after taxes on distributions
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	21.80%
5 Years	rr_AverageAnnualReturnYear05	5.32%
10 Years	rr_AverageAnnualReturnYear10	7.67%
Class I | Putnam Convertible Securities Fund | Class I | after taxes on distributions and sale of fund shares
Prospectus [Line Items]	rr_ProspectusLineItems
1 Year	rr_AverageAnnualReturnYear01	15.56%
5 Years	rr_AverageAnnualReturnYear05	5.18%
10 Years	rr_AverageAnnualReturnYear10	7.05%

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

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

[3] This charge is eliminated after one year.

[4] Performance for class R6 shares prior to their inception (5/22/18) is derived from the historical performance of class Y shares and has not been adjusted for the lower investor servicing fees applicable to class R6 shares; had it, returns would have been higher.