Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FRANKLIN INVESTORS SECURITIES TRUST
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund
Risk/Return:	rr_RiskReturnAbstract
Objective [Heading]	rr_ObjectiveHeading	Investment Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	To maximize income to support monthly distributions, while maintaining the prospects for capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	These tables describe the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts in Class A if you and your family invest, or agree to invest in the future, at least $50,000 in Franklin Templeton funds. More information about these and other discounts is available from your financial professional and under “Your Account” on page 87 in the Fund's Prospectus and under “Buying and Selling Shares” on page 81 of the Fund’s Statement of Additional Information. In addition, more information about sales charge discounts and waivers for purchases of shares through specific financial intermediaries is set forth in Appendix A - "Intermediary Sales Charge Discounts and Waivers" to the Fund's prospectus. Please note that the tables and examples below do not reflect any transaction fees that may be charged by financial intermediaries, or commissions that a shareholder may be required to pay directly to its financial intermediary when buying or selling Class R6 or Advisor Class shares.
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 that 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 costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual Fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 64.69% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	64.69%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts in Class A if you and your family invest, or agree to invest in the future, at least $50,000 in Franklin Templeton funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of the period. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example reflects adjustments made to the Fund's operating expenses due to the fee waivers and/or expense reimbursements by management for the 1 Year numbers only. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If you do not sell your shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal market conditions, the Fund invests in a diversified portfolio of stocks (substantially dividend paying) and debt securities. The Fund normally invests at least 25% of its total assets in debt securities, including bonds, notes, debentures and money market securities. In addition, the Fund normally invests at least 25% of its total assets in equity securities, primarily common and preferred stock. To the extent that the value of convertible and preferred securities can be attributed to their debt characteristics, they will be treated as debt securities for purposes of this investment policy. The Fund seeks income by investing in a combination of corporate, agency and government bonds issued in the United States and other countries, as well as common stocks of companies in any market capitalization range and convertible securities. The Fund seeks capital appreciation by investing in equity securities and convertible securities of companies from a variety of industries. The Fund generally invests in investment grade debt securities. The Fund may invest in debt securities of any duration. The Fund does not currently anticipate investing more than 25% of its total assets in securities of issuers domiciled outside the United States. The Fund also invests in equity-linked notes, which are hybrid derivative-type instruments that are specially designed to combine the characteristics of one or more reference securities (usually a single stock, a stock index or a basket of stocks (underlying securities)) and a related equity derivative, such as a put or call option, in a single note form. The Fund may, from time to time, use (i) equity-related derivatives, which may include call and put options on equity securities and equity security indices, futures on equity securities and equity indexes and options on equity index futures, (ii) interest rate derivatives, including interest rate swaps and interest rate/bond futures contracts, (iii) currency derivatives, including forward foreign currency exchange contracts, currency futures contracts, currency swaps and currency options and (iv) credit-related derivatives, such as credit default swaps and options on credit default swaps for various purposes, including enhancing Fund returns, increasing liquidity, gaining exposure to particular instruments or markets in more efficient or less expensive ways and/or hedging risks. The use of such derivative transactions may allow the Fund to obtain net long or net short exposures to selected securities, markets, interest rates, countries, currencies, credits or durations. The investment manager applies a “bottom-up” approach to investing in individual securities. The investment manager will assess the market price of a company’s securities relative to the investment manager’s evaluation of the company’s long-term earnings, asset value and cash flow potential. The investment manager also considers a company’s price/earnings ratio, profit margins and liquidation value. In determining an optimal mix of equity and fixed-income investments for the Fund, the investment manager assesses changing economic, market and industry conditions. Under normal market conditions, the Fund employs a managed distribution policy that is designed to provide shareholders with regular distributions from their investment. Under this policy, the Fund distributes twelve level monthly payments throughout each calendar year to enable shareholders to estimate the distributions they will receive from the Fund; however, the twelfth monthly payment may be greater than the initially anticipated amount if additional income or capital gains are required to be distributed. The targeted annual payout rate for all share classes is between approximately 2.75% and 6.25% per share based on the last net asset value of the Fund of the prior calendar year in which the distribution is being made (e.g., for distributions made in 2021, the targeted annual payout rate for all share classes will be based on the Fund’s net asset value on December 31, 2020). The distribution rate will vary by class based on the expenses of each class. Every year, the investment manager will undertake to determine if an adjustment should be made to the monthly rate. It is possible to lose money by investing in the Fund notwithstanding the managed distribution policy. There can be no assurance or guarantee that the Fund will provide a fixed stable level of distributions at any time or over any period of time. An investment in the Fund could lose money over short, intermediate, or even long periods of time.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	Under normal market conditions, the Fund invests in a diversified portfolio of stocks (substantially dividend paying) and debt securities.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	You could lose money by investing in the Fund. Mutual fund shares are not deposits or obligations of, or guaranteed or endorsed by, any bank, and are not insured by the Federal Deposit Insurance Corporation, the Federal Reserve Board, or any other agency of the U.S. government. Market The market values of securities or other investments owned by the Fund will go up or down, sometimes rapidly or unpredictably. The market value of a security or other investment may be reduced by market activity or other results of supply and demand unrelated to the issuer. This is a basic risk associated with all investments. When there are more sellers than buyers, prices tend to fall. Likewise, when there are more buyers than sellers, prices tend to rise. The current global outbreak of the novel strain of coronavirus, COVID-19, has resulted in market closures and dislocations, extreme volatility, liquidity constraints and increased trading costs. Efforts to contain the spread of COVID-19 have resulted in global travel restrictions and disruptions of healthcare systems, business operations and supply chains, layoffs, reduced consumer demand, defaults and credit ratings downgrades, and other significant economic impacts. The effects of COVID-19 have impacted global economic activity across many industries and may heighten other pre-existing political, social and economic risks, locally or globally. The full impact of the COVID-19 pandemic is unpredictable and may adversely affect the Fund’s performance. Stock prices tend to go up and down more dramatically than those of debt securities. A slower-growth or recessionary economic environment could have an adverse effect on the prices of the various stocks held by the Fund. Credit An issuer of debt securities may fail to make interest payments or repay principal when due, in whole or in part. Changes in an issuer's financial strength or in a security's or government's credit rating may affect a security's value. Interest Rate When interest rates rise, debt security prices generally fall. The opposite is also generally true: debt security prices rise when interest rates fall. Interest rate changes are influenced by a number of factors, including government policy, monetary policy, inflation expectations, perceptions of risk, and supply of and demand for bonds. In general, securities with longer maturities or durations are more sensitive to interest rate changes. Managed Distribution Policy The Fund's monthly payments under the managed distribution policy may reduce the amount of assets available for investment by the Fund, even if the Fund's assets grow over time. In addition, the Fund may return capital to shareholders (i.e., a return of all or part of a shareholder's original investment). Fund shareholders are expected to receive a monthly distribution that is equal to a set percentage per share, which will be different per class based on differences in class expenses, multiplied by the number of shares owned on the record date; therefore, redemptions from a shareholder’s account will reduce future distributions. The managed distribution policy is not designed to generate, and is not expected to result in, distributions that equal a fixed percentage of the Fund's current net asset value per share or a fixed percentage of a shareholder’s current account value. Equity-Linked Notes (ELNs) ELNs may not perform as expected and could cause the Fund to realize significant losses including its entire principal investment. Other risks include counterparty risk, liquidity risk and imperfect correlation between ELNs and the underlying securities. Convertible Securities Convertible securities are subject to the risks of stocks when the underlying stock price is high relative to the conversion price (because more of the security's value resides in the conversion feature) and debt securities when the underlying stock price is low relative to the conversion price (because the conversion feature is less valuable). A convertible security is not as sensitive to interest rate changes as a similar non-convertible debt security, and generally has less potential for gain or loss than the underlying stock. Management The Fund is subject to management risk because it is an actively managed investment portfolio. The Fund's investment manager applies investment techniques and risk analyses in making investment decisions for the Fund, but there can be no guarantee that these decisions will produce the desired results. Derivative Instruments The performance of derivative instruments depends largely on the performance of an underlying instrument or factor, such as a currency, security, interest rate or index, and such instruments often have risks similar to the underlying instrument, in addition to other risks. Derivatives involve costs and can create economic leverage in the Fund’s portfolio which may result in significant volatility and cause the Fund to participate in losses (as well as gains) in an amount that exceeds the Fund’s initial investment. Other risks include illiquidity, mispricing or improper valuation of the derivative instrument, and imperfect correlation between the value of the derivative and the underlying instrument so that the Fund may not realize the intended benefits. When a derivative is used for hedging, the change in value of the derivative may also not correlate specifically with the currency, security, interest rate, index or other risk being hedged. Derivatives also may present the risk that the other party to the transaction will fail to perform. LIBOR Transition The Fund invests in financial instruments that may have floating or variable rate calculations for payment obligations or financing terms based on the London Interbank Offered Rate (LIBOR), which is the benchmark interest rate at which major global banks lend to one another in the international interbank market for short-term loans. It is currently anticipated that LIBOR will be discontinued by the end of 2021 and will cease to be published after that time (although there are initiatives to delay the discontinuation beyond 2021 for certain LIBOR rates). The impact of the discontinuation of LIBOR and the transition to an alternative rate on the Fund’s portfolio remains uncertain. There can be no guarantee that financial instruments that transition to an alternative reference rate will retain the same value or liquidity as they would otherwise have had. Foreign Securities (non-U.S.) Investing in foreign securities typically involves more risks than investing in U.S. securities, including risks related to currency exchange rates and policies, country or government specific issues, less favorable trading practices or regulation and greater price volatility. Certain of these risks also may apply to securities of U.S. companies with significant foreign operations.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table provide some indication of the risks of investing in the Fund. The bar chart shows changes in the Fund's performance from year to year for Class A shares. The table shows how the Fund's average annual returns for 1 year, 5 years, 10 years or since inception, as applicable, compared with those of a broad measure of market performance. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. You can obtain updated performance information at franklintempleton.com or by calling (800) DIAL BEN/342-5236. The secondary index in the table below shows how the Fund's performance compares to a group of securities that aligns with the fixed-income component of the Fund's portfolio. The blended index in the table below shows how the Fund's performance compares with groups of securities in approximately the same asset class allocations as the Fund. Sales charges are not reflected in the bar chart, and if those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table provide some indication of the risks of investing in the Fund. The bar chart shows changes in the Fund's performance from year to year for Class A shares. The table shows how the Fund's average annual returns for 1 year, 5 years, 10 years or since inception, as applicable, compared with those of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	(800) DIAL BEN/342-5236
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	franklintempleton.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Class A Annual Total Returns
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart, and if those charges were included, returns would be less than those shown.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns(figures reflect sales charges) For the periods ended December 31, 2020
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	No one index is representative of the Fund's portfolio. The figures in the average annual total returns table above reflect the Class A maximum front-end sales charge of 5.50%. Prior to September 10, 2018, Class A shares were subject to a maximum front-end sales charge of 5.75%. If the prior maximum front-end sales charge of 5.75% was reflected, performance for Class A in the average annual total returns table would be lower. The after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of 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 not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown only for Class A and after-tax returns for other classes will vary.
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	5.50%
Maximum Deferred Sales Charge (Load) (as percentage of the lower of original purchase price or sale proceeds)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Management fees	rr_ManagementFeesOverAssets	0.55%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.13%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.94%	[2]
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[3]
Total annual Fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.93%	[2],[3]
1 year	rr_ExpenseExampleYear01	$ 640
3 years	rr_ExpenseExampleYear03	832
5 years	rr_ExpenseExampleYear05	1,041
10 years	rr_ExpenseExampleYear10	$ 1,641
2011	rr_AnnualReturn2011	3.23%
2012	rr_AnnualReturn2012	12.57%
2013	rr_AnnualReturn2013	13.10%
2014	rr_AnnualReturn2014	7.47%
2015	rr_AnnualReturn2015	(2.85%)
2016	rr_AnnualReturn2016	11.98%
2017	rr_AnnualReturn2017	9.51%
2018	rr_AnnualReturn2018	(3.16%)
2019	rr_AnnualReturn2019	17.89%
2020	rr_AnnualReturn2020	5.42%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	9.74%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2020
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(13.37%)
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of the lower of original purchase price or sale proceeds)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Management fees	rr_ManagementFeesOverAssets	0.55%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.13%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.69%	[2]
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[3]
Total annual Fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.68%	[2],[3]
1 year	rr_ExpenseExampleYear01	$ 271
3 years	rr_ExpenseExampleYear03	532
5 years	rr_ExpenseExampleYear05	917
10 years	rr_ExpenseExampleYear10	1,999
1 Year	rr_ExpenseExampleNoRedemptionYear01	171
3 Years	rr_ExpenseExampleNoRedemptionYear03	532
5 Years	rr_ExpenseExampleNoRedemptionYear05	917
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,999
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Class R
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of the lower of original purchase price or sale proceeds)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management fees	rr_ManagementFeesOverAssets	0.55%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	0.13%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.19%	[2]
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[3]
Total annual Fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.18%	[2],[3]
1 year	rr_ExpenseExampleYear01	$ 120
3 years	rr_ExpenseExampleYear03	377
5 years	rr_ExpenseExampleYear05	654
10 years	rr_ExpenseExampleYear10	$ 1,444
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Class R6
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of the lower of original purchase price or sale proceeds)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management fees	rr_ManagementFeesOverAssets	0.55%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.05%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.61%	[2]
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[3]
Total annual Fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.60%	[2],[3]
1 year	rr_ExpenseExampleYear01	$ 61
3 years	rr_ExpenseExampleYear03	194
5 years	rr_ExpenseExampleYear05	339
10 years	rr_ExpenseExampleYear10	$ 762
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Advisor Class
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of the lower of original purchase price or sale proceeds)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management fees	rr_ManagementFeesOverAssets	0.55%
Distribution and service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.13%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.69%	[2]
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[3]
Total annual Fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.68%	[2],[3]
1 year	rr_ExpenseExampleYear01	$ 69
3 years	rr_ExpenseExampleYear03	220
5 years	rr_ExpenseExampleYear05	383
10 years	rr_ExpenseExampleYear10	$ 858
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Return Before Taxes | Class A
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
Past 1 year	rr_AverageAnnualReturnYear01	(0.37%)
Past 5 years	rr_AverageAnnualReturnYear05	6.89%
Past 10 years	rr_AverageAnnualReturnYear10	6.70%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Return Before Taxes | Class C
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	3.60%
Past 5 years	rr_AverageAnnualReturnYear05	7.29%
Past 10 years	rr_AverageAnnualReturnYear10	6.54%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Return Before Taxes | Class R
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	5.14%
Past 5 years	rr_AverageAnnualReturnYear05	7.82%
Past 10 years	rr_AverageAnnualReturnYear10	7.08%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Return Before Taxes | Class R6
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	5.70%
Past 5 years	rr_AverageAnnualReturnYear05	8.48%
Since Inception	rr_AverageAnnualReturnSinceInception	7.14%	[4]
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Return Before Taxes | Advisor Class
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	5.62%
Past 5 years	rr_AverageAnnualReturnYear05	8.36%
Past 10 years	rr_AverageAnnualReturnYear10	7.61%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | After Taxes on Distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
Past 1 year	rr_AverageAnnualReturnYear01	(1.85%)
Past 5 years	rr_AverageAnnualReturnYear05	5.26%
Past 10 years	rr_AverageAnnualReturnYear10	5.30%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | After Taxes on Distributions and Sales | Class A
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares
Past 1 year	rr_AverageAnnualReturnYear01	0.08%
Past 5 years	rr_AverageAnnualReturnYear05	4.90%
Past 10 years	rr_AverageAnnualReturnYear10	4.92%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Blended (50% MSCI USA High Dividend Yield Index + 25% ICE BofA U.S. Corporate & High Yield Index + 25% Bloomberg Barclays U.S. Aggregate Index) (index reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	5.50%
Past 5 years	rr_AverageAnnualReturnYear05	8.59%
Past 10 years	rr_AverageAnnualReturnYear10	8.68%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | Bloomberg Barclays U.S. Aggregate Index (index reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	7.51%
Past 5 years	rr_AverageAnnualReturnYear05	4.43%
Past 10 years	rr_AverageAnnualReturnYear10	3.84%
Franklin Investors Securities Trust - FIST1-32 | Franklin Managed Income Fund | S&P 500 Index (index reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
Past 1 year	rr_AverageAnnualReturnYear01	18.40%
Past 5 years	rr_AverageAnnualReturnYear05	15.21%
Past 10 years	rr_AverageAnnualReturnYear10	13.88%

[1] 1. There is a 1% contingent deferred sales charge that applies to investments of $1 million or more (see "Investments of $1 Million or More" under "Choosing a Share Class") and purchases by certain retirement plans without an initial sales charge on shares sold within 18 months of purchase.

[2] 1. Total annual Fund operating expenses differ from the ratio of expenses to average net assets shown in the Financial Highlights, which reflect the operating expenses of the Fund and do not include acquired fund fees and expenses.

[3] 2. The investment manager has contractually agreed to waive or assume certain expenses so that total annual Fund operating expenses (excluding Rule 12b-1 fees and certain non-routine expenses) and acquired fund fees and expenses for each class of the Fund do not exceed 0.68%, until February 28, 2022. In addition, the transfer agent has contractually agreed to limit its fees on Class R6 shares to 0.03% until February 28, 2022. The investment manager also has contractually agreed in advance to reduce its fees as a result of the Fund's investment in Franklin Templeton affiliated funds (acquired fund) for at least one year following the date of this prospectus. Contractual fee waiver and/or expense reimbursement agreements may not be changed or terminated during the time period set forth above.

[4] 1. Since inception May 1, 2013.