485BPOS

	As filed with the Securities and Exchange Commission on
	March 12, 2018
	Registration No. 002-43384
	811-02280
	SECURITIES AND EXCHANGE COMMISSION
	WASHINGTON, D.C. 20549
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	FORM N-1A
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	REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933	/ X /
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	Pre-Effective Amendment No.	/    /
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	Post-Effective Amendment No. 66	/ X /
	and/or	----
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	REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY	/ X /
	ACT OF 1940	----
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	Amendment No. 58	/ X /
	(Check appropriate box or boxes)	----
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	PUTNAM CONVERTIBLE SECURITIES FUND
	(Exact Name of Registrant as Specified in Charter)
	One Post Office Square, Boston, Massachusetts 02109
	(Address of Principal Executive Offices) (Zip Code)
	Registrant's Telephone Number, including Area Code
	(617) 292-1000
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	It is proposed that this filing will become effective
	(check appropriate box)
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/    /	immediately upon filing pursuant to paragraph (b)
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/ X /	on February 28, 2018 pursuant to paragraph (b)
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/    /	60 days after filing pursuant to paragraph (a)(1)
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/    /	on (date) pursuant to paragraph (a)(1)
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/    /	75 days after filing pursuant to paragraph (a)(2)
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/    /	on (date) pursuant to paragraph (a)(2) of Rule 485.
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If appropriate, check the following box:
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/    /	this post-effective amendment designates a new
----	effective date for a previously filed post-effective amendment.
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	ROBERT T. BURNS, Vice President
	PUTNAM CONVERTIBLE SECURITIES FUND
	One Post Office Square
	Boston, Massachusetts 02109
	(Name and address of agent for service)
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	Copy to:
	BRYAN CHEGWIDDEN, Esquire
	ROPES & GRAY LLP
	1211 Avenue of the Americas
	New York, New York 10036

PUTNAM CONVERTIBLE SECURITIES FUND

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement under Rule 485(b) under the Securities Act of 1933, as amended, and has duly caused this Amendment to its Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of Boston, and The Commonwealth of Massachusetts, on the 12^th day of March, 2018.

Putnam Convertible Securities Fund

By: /s/ Jonathan S. Horwitz, Executive Vice President, Principal Executive Officer and Compliance Liaison

Pursuant to the requirements of the Securities Act of 1933, as amended, this Amendment to the Registration Statement has been signed below by the following persons in the capacities and on the date indicated:

Signature Title

Jameson A. Baxter * Chair, Board of Trustees

Kenneth R. Leibler* Vice Chair, Board of Trustees

Robert L. Reynolds* President and Trustee

Jonathan S. Horwitz* Executive Vice President, Principal Executive

Officer and Compliance Liaison

Janet C. Smith* Vice President, Principal Financial Officer, Principal Accounting Officer and Assistant Treasurer

Liaquat Ahamed* Trustee

Ravi Akhoury* Trustee

Barbara M. Baumann* Trustee

Katinka Domotorffy* Trustee

Catharine Bond Hill* Trustee

Paul L. Joskow* Trustee

Robert E. Patterson* Trustee

George Putnam, III* Trustee

Manoj P. Singh* Trustee

By:   /s/Jonathan S. Horwitz, as Attorney-in-Fact

March 12, 2018

*Signed pursuant to power of attorney filed in Post-Effective Amendment No. 65 to the Registrant's Registration Statement on February 28, 2018.

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Class A B C M R T Y | Putnam Convertible Securities Fund

Fund Summary

Goal

Putnam Convertible Securities Fund seeks, with equal emphasis, current income and capital appreciation.

Its secondary objective is conservation of capital.

Fees and expenses

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 13 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 (fees paid directly from your investment)

Shareholder Fees - Class A B C M R T Y - Putnam Convertible Securities Fund	Class A		Class B		Class C		Class M	Class R	Class T	Class Y
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	5.75%		none		none		3.50%	none	2.50%	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none

Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - Class A B C M R T Y - Putnam Convertible Securities Fund	Class A	Class B	Class C	Class M	Class R	Class T		Class Y
Management fees	0.63%	0.63%	0.63%	0.63%	0.63%	0.63%		0.63%
Distribution and service (12b-1) fees	0.25%	1.00%	1.00%	0.75%	0.50%	0.25%
Other expenses	0.19%	0.19%	0.19%	0.19%	0.19%	0.19%	[1]	0.19%
Total annual fund operating expenses	1.07%	1.82%	1.82%	1.57%	1.32%	1.07%		0.82%

Example

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.

Expense Example - Class A B C M R T Y - Putnam Convertible Securities Fund - USD ($)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
Class A	678	896	1,131	1,806
Class B	685	873	1,185	1,940
Class C	285	573	985	2,137
Class M	504	828	1,175	2,152
Class R	134	418	723	1,590
Class T	356	582	825	1,523
Class Y	84	262	455	1,014

Expense Example, No Redemption - Class A B C M R T Y - Putnam Convertible Securities Fund - USD ($)	Expense Example, No Redemption, 1 Year	Expense Example, No Redemption, 3 Years	Expense Example, No Redemption, 5 Years	Expense Example, No Redemption, 10 Years
Class B	185	573	985	1,940
Class C	185	573	985	2,137

Portfolio turnover

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 56%.

Investments, risks, and performance

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.

Risks

It is important to understand that you can lose money by investing in the fund.

The value of convertible securities 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 (including perceptions about the risk of default and expectations about monetary policy or interest rates), 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. 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.

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.

Performance

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.

Annual total returns for class A shares before sales charges

Best calendar quarter
Q2 2009   19.05%

Worst calendar quarter
Q4 2008 −26.03%

Average annual total returns after sales charges
(for periods ending 12/31/17)

Average Annual Total Returns - Class A B C M R T Y - Putnam Convertible Securities Fund		1 Year	5 Years	10 Years
Class A		8.32%	7.65%	5.64%
Class A | after taxes on distributions		7.07%	6.27%	4.51%
Class A | after taxes on distributions and sale of fund shares		5.26%	5.56%	4.09%
Class B		9.10%	7.83%	5.63%
Class C		13.09%	8.12%	5.48%
Class M		10.32%	7.62%	5.36%
Class R		14.61%	8.66%	6.00%
Class T	[1]	12.06%	8.38%	6.00%
Class Y		15.24%	9.21%	6.54%
ICE BofAML U.S. Convertible Index (no deduction for fees, expenses or taxes)		13.70%	10.74%	7.35%

ICE BofAML Indexes: ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML 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 BofAML 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.

[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.

[1] Other expenses are based on expenses of class A shares for the fund's last fiscal year.

[1] 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.

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Putnam Convertible Securities Fund | Class I

Fund Summary

Goal

Putnam Convertible Securities Fund seeks, with equal emphasis, current income and capital appreciation.

Its secondary objective is conservation of capital.

Fees and expenses

The following table describes the fees and expenses you may pay if you buy and hold Class I shares of the fund.

Shareholder fees (fees paid directly from your investment)

Shareholder Fees	Class I Putnam Convertible Securities Fund Class I
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	none

Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Class I Putnam Convertible Securities Fund Class I
Management fees	0.63%
Distribution and service (12b-1) fees
Other expenses	0.06%
Total annual fund operating expenses	0.69%

Example

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.

Expense Example	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
Class I | Putnam Convertible Securities Fund | Class I | USD ($)	70	221	384	859

Portfolio turnover

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 56%.

Investments, risks, and performance

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.

Risks

It is important to understand that you can lose money by investing in the fund.

The value of convertible securities 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 (including perceptions about the risk of default and expectations about monetary policy or interest rates), 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. 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.

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.

Performance

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 before their inception (3/3/15) is derived from the historical performance of the fund’s class Y shares, which are not offered in this prospectus, and has not been adjusted to reflect the lower fees associated with class I shares; had it, returns would have been higher. Please remember that past performance is not necessarily an indication of future results

Annual total returns for class I shares

Best calendar quarter
Q3 2016  6.86%

Worst calendar quarter
Q1 2016 −1.28%

Average annual total returns (for periods ending 12/31/17)

Average Annual Total Returns - Class I - Putnam Convertible Securities Fund	1 Year	5 Years	10 Years
Class I	15.42%	9.30%	6.58%
Class I | after taxes on distributions	13.92%	7.70%	5.31%
Class I | after taxes on distributions and sale of fund shares	9.34%	6.76%	4.79%
ICE BofAML U.S. Convertible Index (no deduction for fees, expenses or taxes)	13.70%	10.74%	7.35%

ICE BofAML Indexes: ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML 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 BofAML 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.

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Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2017
Registrant Name	dei_EntityRegistrantName	PUTNAM CONVERTIBLE SECURITIES FUND
Central Index Key	dei_EntityCentralIndexKey	0000081247
Amendment Flag	dei_AmendmentFlag	false
Trading Symbol	dei_TradingSymbol	PCONX
Document Creation Date	dei_DocumentCreationDate	Feb. 28, 2018
Document Effective Date	dei_DocumentEffectiveDate	Feb. 28, 2018
Prospectus Date	rr_ProspectusDate	Feb. 28, 2018
Class A B C M R T Y | Putnam Convertible Securities Fund
Risk Return Abstract	rr_RiskReturnAbstract
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 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 13 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 56%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	56.00%
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 13 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 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 convertible securities 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 (including perceptions about the risk of default and expectations about monetary policy or interest rates), 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. 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. 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 Q2 2009   19.05% Worst calendar quarter Q4 2008 −26.03%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best calendar quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	19.05%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst calendar quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(26.03%)
Performance Table Heading	rr_PerformanceTableHeading	Average annual total returns after sales charges (for periods ending 12/31/17)
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 BofAML Indexes: ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML 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 BofAML 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 M R T Y | Putnam Convertible Securities 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	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.07%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 678
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	896
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,131
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,806
Annual Return 2008	rr_AnnualReturn2008	(39.46%)
Annual Return 2009	rr_AnnualReturn2009	53.75%
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%
1 Year	rr_AverageAnnualReturnYear01	8.32%
5 Years	rr_AverageAnnualReturnYear05	7.65%
10 Years	rr_AverageAnnualReturnYear10	5.64%
Class A B C M R T Y | Putnam Convertible Securities 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%	[2]
Management fees	rr_ManagementFeesOverAssets	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.82%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 685
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	873
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,185
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,940
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	185
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	573
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	985
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,940
1 Year	rr_AverageAnnualReturnYear01	9.10%
5 Years	rr_AverageAnnualReturnYear05	7.83%
10 Years	rr_AverageAnnualReturnYear10	5.63%
Class A B C M R T Y | Putnam Convertible Securities 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%	[3]
Management fees	rr_ManagementFeesOverAssets	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.82%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 285
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	573
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	985
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,137
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	185
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	573
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	985
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,137
1 Year	rr_AverageAnnualReturnYear01	13.09%
5 Years	rr_AverageAnnualReturnYear05	8.12%
10 Years	rr_AverageAnnualReturnYear10	5.48%
Class A B C M R T Y | Putnam Convertible Securities 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	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.57%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 504
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	828
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,175
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 2,152
1 Year	rr_AverageAnnualReturnYear01	10.32%
5 Years	rr_AverageAnnualReturnYear05	7.62%
10 Years	rr_AverageAnnualReturnYear10	5.36%
Class A B C M R T Y | Putnam Convertible Securities 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	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.32%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 134
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	418
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	723
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,590
1 Year	rr_AverageAnnualReturnYear01	14.61%
5 Years	rr_AverageAnnualReturnYear05	8.66%
10 Years	rr_AverageAnnualReturnYear10	6.00%
Class A B C M R T Y | Putnam Convertible Securities 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	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.19%	[4]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.07%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 356
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	582
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	825
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,523
1 Year	rr_AverageAnnualReturnYear01	12.06%	[5]
5 Years	rr_AverageAnnualReturnYear05	8.38%	[5]
10 Years	rr_AverageAnnualReturnYear10	6.00%	[5]
Class A B C M R T Y | Putnam Convertible Securities 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	0.63%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.82%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 84
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	262
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	455
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,014
1 Year	rr_AverageAnnualReturnYear01	15.24%
5 Years	rr_AverageAnnualReturnYear05	9.21%
10 Years	rr_AverageAnnualReturnYear10	6.54%
Class A B C M R T Y | Putnam Convertible Securities Fund | after taxes on distributions | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	7.07%
5 Years	rr_AverageAnnualReturnYear05	6.27%
10 Years	rr_AverageAnnualReturnYear10	4.51%
Class A B C M R T Y | Putnam Convertible Securities Fund | after taxes on distributions and sale of fund shares | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.26%
5 Years	rr_AverageAnnualReturnYear05	5.56%
10 Years	rr_AverageAnnualReturnYear10	4.09%
Class A B C M R T Y | Putnam Convertible Securities Fund | ICE BofAML U.S. Convertible Index (no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.70%
5 Years	rr_AverageAnnualReturnYear05	10.74%
10 Years	rr_AverageAnnualReturnYear10	7.35%
Class I | Putnam Convertible Securities Fund
Risk Return Abstract	rr_RiskReturnAbstract
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 table describes 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 56%.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	56.00%
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 Investments
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	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 convertible securities 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 (including perceptions about the risk of default and expectations about monetary policy or interest rates), 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. 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. 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 before their inception (3/3/15) is derived from the historical performance of the fund’s class Y shares, which are not offered in this prospectus, and has not been adjusted to reflect the lower fees associated with 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 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 Closing [Text Block]	rr_BarChartClosingTextBlock	Best calendar quarter Q3 2016  6.86% Worst calendar quarter Q1 2016 −1.28%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best calendar quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2016
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	6.86%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst calendar quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 30, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.28%)
Performance Table Heading	rr_PerformanceTableHeading	Average annual total returns (for periods ending 12/31/17)
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 Closing [Text Block]	rr_PerformanceTableClosingTextBlock	ICE BofAML Indexes: ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML 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 BofAML 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 | Class I
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	0.63%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets
Other expenses	rr_OtherExpensesOverAssets	0.06%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.69%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 70
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	221
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	384
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 859
Annual Return 2016	rr_AnnualReturn2016	9.95%
Annual Return 2017	rr_AnnualReturn2017	15.42%
1 Year	rr_AverageAnnualReturnYear01	15.42%
5 Years	rr_AverageAnnualReturnYear05	9.30%
10 Years	rr_AverageAnnualReturnYear10	6.58%
Class I | Putnam Convertible Securities Fund | after taxes on distributions | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.92%
5 Years	rr_AverageAnnualReturnYear05	7.70%
10 Years	rr_AverageAnnualReturnYear10	5.31%
Class I | Putnam Convertible Securities Fund | after taxes on distributions and sale of fund shares | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	9.34%
5 Years	rr_AverageAnnualReturnYear05	6.76%
10 Years	rr_AverageAnnualReturnYear10	4.79%
Class I | Putnam Convertible Securities Fund | ICE BofAML U.S. Convertible Index (no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.70%
5 Years	rr_AverageAnnualReturnYear05	10.74%
10 Years	rr_AverageAnnualReturnYear10	7.35%

[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] Other expenses are based on expenses of class A shares for the fund's last fiscal year.

[5] 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.