2.4.0.8010000 - Document - Risk/Return Summary {Unlabeled}falsefalsetrue1false falsefalseThttp://www.sec.gov/CIK0000809707duration2013-09-20T00:00:002013-09-20T00:00:001false 2rr_RiskReturnHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Fund Summaryfalsefalsefalsexbrli:stringItemTypestringRisk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicatedReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 false0Risk/Return [Heading]2false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00Franklin Adjustable U.S. Government Securities Fundfalsefalsefalse2false truefalseS000006850http://www.sec.gov/CIK0000809707duration2013-09-20T00:00:002013-09-20T00:00:00falsefalsefist_S000006850Memberdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMembernanafalse0Franklin Adjustable U.S. Government Securities Fund3false 2rr_ObjectiveHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Investment Goalfalsefalsefalsexbrli:stringItemTypestringInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a false0Objective [Heading]4false 2rr_ObjectivePrimaryTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00High level of current income, while providing lower volatility of principal than a fund that invests in fixed-rate securities.falsefalsefalsenonnum:textBlockItemTypenaInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a false0Objective, Primary [Text Block]5false 2rr_ExpenseHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Fees and Expenses of the Fundfalsefalsefalsexbrli:stringItemTypestringRisk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared 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 $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example 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 you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. 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 __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 1 -Subparagraph d false0Expense [Heading]6false 2rr_ExpenseNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00These 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 $100,000 in Franklin Templeton funds. More information about these and other discounts is available from your financial professional and under “Your Account” on page 113 in the Fund's Prospectus and under “Buying and Selling Shares” on page 75 of the Fund’s Statement of Additional Information.falsefalsefalsenonnum:textBlockItemTypenaThis table describes the fees and expenses that you may pay if you buy and hold shared 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 $[_____] in [name of fund family] funds. Include the narrative explanations in the order indicated. A Fund may modify the narrative explanations if the explanation contains comparable information to that shown. The narrative explanation regarding sales charge discounts is only required by a Fund that offers such discounts and should specify the minimum level of investment required to qualify for a discount. Modify the narrative explanation to state that Fund shares are sold on a national securities exchange at the end of the time periods indicated, and that brokerage commissions for buying and selling Fund shares through a broker are not reflected.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 1 -Subparagraph b false0Expense Narrative [Text Block]7false 2rr_ShareholderFeesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00SHAREHOLDER FEES (fees paid directly from your investment)falsefalsefalsexbrli:stringItemTypestringShareholder Fees (fees paid directly from your investment).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 false0Shareholder Fees Caption [Text]8false 2rr_ShareholderFeesTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/ShareholderFeesData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsefalse~ http://xbrl.sec.gov/rr/role/ShareholderFeesData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsehttp://xbrl.sec.gov/rr/role/ShareholderFeesData020010 - Schedule - Shareholder Feestruefalsefalse1falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass ARatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$2falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Crr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018510Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass CRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$3falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass R6rr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000133492Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass R6RatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$4falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseAdvisor Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000064441Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundAdvisor ClassRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$1falseRowprimaryElement*3false 2rr_MaximumCumulativeSalesChargeOverOfferingPricerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4TypepureMaximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price). If a sales charge (load) is imposed on shares purchased with reinvested capital gains distributions or returns of capital, include the bracketed words in the third caption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 1 false0Maximum Cumulative Sales Charge (as a percentage of Offering Price) 0rr_MaximumCumulativeSalesChargeOverOfferingPricerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.02250.0225falsefalsefalse2truetruetrue0.000.00falsefalsefalse3truetruetrue0.000.00[1]falsefalsefalse4truetruetrue0.000.00falsefalsefalserr:NonNegativePure4TypepureMaximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price). If a sales charge (load) is imposed on shares purchased with reinvested capital gains distributions or returns of capital, include the bracketed words in the third caption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 1 false0Maximum Cumulative Sales Charge (as a percentage of Offering Price)2falseRowprimaryElement*4false 2rr_MaximumDeferredSalesChargeOverOfferingPricerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4TypepureMaximum Deferred Sales Charge (Load) (as a percentage of ____) A.3.instructions.2.a.i "Maximum Deferred Sales Charge (Load)" includes the maximum total deferred sales charge (load) payable upon redemption, in installments, or both, expressed as a percentage of the amount or amounts stated in response to Item 7(a), except that, for a sales charge (load) based on net asset value at the time of purchase, show the sales charge (load) as a percentage of the offering price at the time of purchase. A Fund may include in a footnote to the table, if applicable, a tabular presentation showing the amount of deferred sales charges (loads) over time or a narrative explanation of the sales charges (loads) (e.g., __% in the first year after purchase, declining to __% in the __ year and eliminated thereafter). A.3.instructions.2.a.ii If more than one type of sales charge (load) is imposed (e.g., a deferred sales charge (load) and a front-end sales charge (load)), the first caption in the table should read "Maximum Sales Charge (Load)" and show the maximum cumulative percentage. Show the percentage amounts and the terms of each sales charge (load) comprising that figure on separate lines below.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 2 -Subparagraph a -Clause i false0Maximum Deferred Sales Charge (as a percentage of Offering Price) 0rr_MaximumDeferredSalesChargeOverOfferingPricerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.000.00falsefalsefalse2truetruetrue0.01000.0100falsefalsefalse3truetruetrue0.000.00[1]falsefalsefalse4truetruetrue0.000.00falsefalsefalserr:NonNegativePure4TypepureMaximum Deferred Sales Charge (Load) (as a percentage of ____) A.3.instructions.2.a.i "Maximum Deferred Sales Charge (Load)" includes the maximum total deferred sales charge (load) payable upon redemption, in installments, or both, expressed as a percentage of the amount or amounts stated in response to Item 7(a), except that, for a sales charge (load) based on net asset value at the time of purchase, show the sales charge (load) as a percentage of the offering price at the time of purchase. A Fund may include in a footnote to the table, if applicable, a tabular presentation showing the amount of deferred sales charges (loads) over time or a narrative explanation of the sales charges (loads) (e.g., __% in the first year after purchase, declining to __% in the __ year and eliminated thereafter). A.3.instructions.2.a.ii If more than one type of sales charge (load) is imposed (e.g., a deferred sales charge (load) and a front-end sales charge (load)), the first caption in the table should read "Maximum Sales Charge (Load)" and show the maximum cumulative percentage. Show the percentage amounts and the terms of each sales charge (load) comprising that figure on separate lines below.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 2 -Subparagraph a -Clause i false0Maximum Deferred Sales Charge (as a percentage of Offering Price)1The Fund will begin offering Class R6 shares on September 20, 2013.falseShareholder Fees Franklin Adjustable U.S. Government Securities FundUnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet426442018ColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to ShareholderFeesData.No definition available.false0Shareholder Fees [Table]9false 2rr_OperatingExpensesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>ANNUAL FUND OPERATING EXPENSES</p><p>(expenses that you pay each year as a percentage of the value of your investment)</p></div>falsefalsefalsexbrli:stringItemTypestringAnnual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investment)Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 7 false0Operating Expenses Caption [Text]10false 2rr_AnnualFundOperatingExpensesTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/OperatingExpensesData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsefalse~ http://xbrl.sec.gov/rr/role/OperatingExpensesData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsehttp://xbrl.sec.gov/rr/role/OperatingExpensesData020020 - Schedule - Annual Fund Operating Expensestruefalsefalse1falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass ARatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$2falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Crr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018510Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass CRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$3falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass R6rr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000133492Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass R6RatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$4falseColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseAdvisor Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000064441Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundAdvisor ClassRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$1falseRowprimaryElement*3false 2rr_ManagementFeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4TypepureManagement Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph a false0Management Fees (as a percentage of Assets) 0rr_ManagementFeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00500.0050falsefalsefalse2truetruetrue0.00500.0050falsefalsefalse3truetruetrue0.00500.0050falsefalsefalse4truetruetrue0.00500.0050falsefalsefalserr:NonNegativePure4TypepureManagement Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph a false0Management Fees (as a percentage of Assets)2falseRowprimaryElement*4false 2rr_DistributionAndService12b1FeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4TypepureDistribution [and/or Service] (12b-1) Fees" include all distribution or other expenses incurred during the most recent fiscal year under a plan adopted pursuant to rule 12b-1 [17 CFR 270.12b-1]. Under an appropriate caption or a subcaption of "Other Expenses," disclose the amount of any distribution or similar expenses deducted from the Fund's assets other than pursuant to a rule 12b-1 plan.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 9 false0Distribution and Service (12b-1) Fees 0rr_DistributionAndService12b1FeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00250.0025falsefalsefalse2truetruetrue0.00650.0065falsefalsefalse3truetruetrue0.000.00falsefalsefalse4truetruetrue0.000.00falsefalsefalserr:NonNegativePure4TypepureDistribution [and/or Service] (12b-1) Fees" include all distribution or other expenses incurred during the most recent fiscal year under a plan adopted pursuant to rule 12b-1 [17 CFR 270.12b-1]. Under an appropriate caption or a subcaption of "Other Expenses," disclose the amount of any distribution or similar expenses deducted from the Fund's assets other than pursuant to a rule 12b-1 plan.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 9 false0Distribution and Service (12b-1) Fees3falseRowprimaryElement*5false 2rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4Typepure"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph c -Clause i false0Other Expenses (as a percentage of Assets): 0rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse[1]1truetruetrue0.00120.0012falsefalsefalse2truetruetrue0.00120.0012falsefalsefalse3truetruetrue0.00040.0004falsefalsefalse4truetruetrue0.00120.0012falsefalsefalserr:NonNegativePure4Typepure"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph c -Clause i false0Other Expenses (as a percentage of Assets):4falseRowprimaryElement*6false 2rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph d false0Expenses (as a percentage of Assets) 0rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00870.0087falsefalsefalse2truetruetrue0.01270.0127falsefalsefalse3truetruetrue0.00540.0054falsefalsefalse4truetruetrue0.00620.0062falsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph d false0Expenses (as a percentage of Assets)1Other expenses for Class R6 represent an estimate of expenses, including the effect of this Class's lower shareholder servicing fees.falseAnnual Fund Operating Expenses Franklin Adjustable U.S. Government Securities FundUnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet44121244026ColumnperiodPeriod*Columndei_LegalEntityAxisAxisfist_S000006850MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to OperatingExpensesData.No definition available.false0Annual Fund Operating Expenses [Table]11false 2rr_ExpenseExampleHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Examplefalsefalsefalsexbrli:stringItemTypestringHeading for Expense Example.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 false0Expense Example [Heading]12false 2rr_ExpenseExampleNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00This 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 waiver and/or expense reimbursement 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:falsefalsefalsenonnum:textBlockItemTypenaThe Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 1 false0Expense Example Narrative [Text Block]13false 2rr_ExpenseExampleWithRedemptionTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/ExpenseExample column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsefalse~ http://xbrl.sec.gov/rr/role/ExpenseExample column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~truehttp://xbrl.sec.gov/rr/role/ExpenseExample020030 - Schedule - Expense Example {Transposed}truefalsefalse1falseColumnprimaryElement*3false 2rr_ExpenseExampleYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 false2Expense Example, with Redemption, 1 Year USDfalsefalse$2falseColumnprimaryElement*4false 2rr_ExpenseExampleYear03rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false2Expense Example, with Redemption, 3 Years USDfalsefalse$3falseColumnprimaryElement*5false 2rr_ExpenseExampleYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false2Expense Example, with Redemption, 5 Years USDfalsefalse$4falseColumnprimaryElement*6false 2rr_ExpenseExampleYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. 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Include the second 1-, 3-, 5-, and 10-year periods and related narrative explanation only if a sales charge (load) or other fee is charged upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 2 -Subparagraph 1 false0Expense Example, No Redemption, By Year, Caption [Text]15false 2rr_ExpenseExampleNoRedemptionTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~falsefalse~ http://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * row primary compact * ~truehttp://xbrl.sec.gov/rr/role/ExpenseExampleNoRedemption020040 - Schedule - Expense Example, No Redemption {Transposed}truefalsefalse1falseColumnprimaryElement*3false 2rr_ExpenseExampleNoRedemptionYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryYou would pay the following expenses if you did not redeem your shares. Include the second 1-, 3-, 5-, and 10-year periods and related narrative explanation only if a sales charge (load) or other fee is charged upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 2 -Subparagraph 1 false2Expense Example, No Redemption, 1 Year USDfalsefalse$2falseColumnprimaryElement*4false 2rr_ExpenseExampleNoRedemptionYear03rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryYou would pay the following expenses if you did not redeem your shares. Include the second 1-, 3-, 5-, and 10-year periods and related narrative explanation only if a sales charge (load) or other fee is charged upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 2 -Subparagraph 1 false2Expense Example, No Redemption, 3 Years USDfalsefalse$3falseColumnprimaryElement*5false 2rr_ExpenseExampleNoRedemptionYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryYou would pay the following expenses if you did not redeem your shares. Include the second 1-, 3-, 5-, and 10-year periods and related narrative explanation only if a sales charge (load) or other fee is charged upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 -Subparagraph f false2Expense Example, No Redemption, 5 Years USDfalsefalse$4falseColumnprimaryElement*6false 2rr_ExpenseExampleNoRedemptionYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalserr:NonNegativeMonetaryTypemonetaryYou would pay the following expenses if you did not redeem your shares. Include the second 1-, 3-, 5-, and 10-year periods and related narrative explanation only if a sales charge (load) or other fee is charged upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 -Subparagraph f false2Expense Example, No Redemption, 10 Years USDfalsefalse$1falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Crr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018510Memberrr_ProspectusShareClassAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass CUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170 0truefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue129129falsefalsefalse2truefalsetrue403403falsefalsefalse3truefalsetrue697697falsefalsefalse4truefalsetrue15341534falsefalsefalsenanafalse0Franklin Adjustable U.S. Government Securities Fund Class CfalseExpense Example, No Redemption (USD $)UnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet413041020ColumnprimaryElement*RowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*RowunitUnit*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to ExpenseExampleNoRedemption.No definition available.false0Expense Example, No Redemption [Table]16false 2rr_PortfolioTurnoverHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Portfolio Turnoverfalsefalsefalsexbrli:stringItemTypestringDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 5 false0Portfolio Turnover [Heading]17false 2rr_PortfolioTurnoverTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>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 4.87% of the average value of its portfolio.</p></div>falsefalsefalsenonnum:textBlockItemTypenaDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 3 false0Portfolio Turnover [Text Block]18false 2rr_StrategyHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Principal Investment Strategiesfalsefalsefalsexbrli:stringItemTypestringPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy [Heading]19false 2rr_StrategyNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>Under normal market conditions, the Fund invests at least 80% of its net assets in &#147;adjustable-rate U.S. government mortgage securities.&#148; &#147;Adjustable-rate U.S. government mortgage securities&#148; include adjustable-rate mortgage securities (ARMS) and other mortgage-backed securities with interest rates that adjust periodically to reflect prevailing market interest rates, which are issued or guaranteed by the U.S. government, its agencies or instrumentalities, including government sponsored entities.</p><p>Mortgage-backed securities represent an interest in a pool of mortgage loans made by banks and other financial institutions to finance purchases of homes, commercial buildings and other real estate. As the underlying mortgage loans are paid off, investors receive periodic principal and interest payments as well as any unscheduled principal prepayments on the underlying mortgage loans. The mortgage-backed securities purchased by the Fund include bonds and notes issued or guaranteed by the Government National Mortgage Association (Ginnie Mae) and U.S. government-sponsored entities, such as the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac). The Fund currently focuses on mortgage-backed securities issued or guaranteed by Fannie Mae and Freddie Mac.</p><p>Government agency or instrumentality issues have different levels of credit support. Ginnie Mae pass-through mortgage certificates are backed by the full faith and credit of the U.S. government. <b>U.S. government-sponsored entities, such as Fannie Mae and Freddie Mac, may be chartered by Acts of Congress, but their securities are neither issued nor guaranteed by the U.S. government. Although the U.S. government has provided financial support to Fannie Mae and Freddie Mac, no assurance can be given that the U.S. government will continue to do so.</b> Accordingly, securities issued by Fannie Mae and Freddie Mac may involve a risk of non-payment of principal and interest. Investors should remember that guarantees of timely prepayment of principal and interest do not apply to the market prices and yields of the securities or to the net asset value or performance of the Fund, which will vary with changes in interest rates and other market conditions. Any downgrade of the credit rating of the securities issued by the U.S. government may result in a downgrade of securities issued by its agencies or instrumentalities, including government-sponsored entities.</p><p>These periodic interest rate adjustments may help keep the prices of these securities relatively stable when compared with the prices of fixed-rate securities, which generally fall when interest rates rise. Adjustable-rate securities, however, frequently limit the maximum amount by which the interest rate may change up or down. The Fund, therefore, may not benefit from increases in interest rates if interest rates exceed a security&#146;s maximum allowable periodic or lifetime limits. During periods of falling interest rates, the interest rates on these securities may reset downward, resulting in a lower yield for the Fund.</p><p>The Fund may invest up to 20% of its net assets in other securities, including fixed-rate mortgage-backed securities, mortgage-backed securities issued by a private entity, direct obligations of the U.S. government, such as Treasury bills, bonds or notes, and in repurchase agreements collateralized by U.S. government or government agency securities.</p></div>falsefalsefalsenonnum:textBlockItemTypenaPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy Narrative [Text Block]20false 2rr_RiskHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Principal Risksfalsefalsefalsexbrli:stringItemTypestringNarrative Risk Disclosure.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 false0Risk [Heading]21false 2rr_RiskNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>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.</p><p>Interest Rate</p><p>When interest rates rise, debt security prices generally fall. The opposite is also generally true: debt security prices rise when interest rates fall. In general, securities with longer maturities are more sensitive to these interest rate changes.</p><p>Mortgage-Backed Securities</p><p>Mortgage-backed securities differ from conventional debt securities because principal is paid back periodically over the life of the security rather than at maturity. The Fund may receive unscheduled payments of principal due to voluntary prepayments, refinancings or foreclosures on the underlying mortgage loans. Because of prepayments, mortgage-backed securities may be less effective than some other types of debt securities as a means of "locking in" long-term interest rates and may have less potential for capital appreciation during periods of falling interest rates. A reduction in the anticipated rate of principal prepayments, especially during periods of rising interest rates, may increase or extend the effective maturity of mortgage-backed securities, making them more sensitive to interest rate changes, subject to greater price volatility, and more susceptible than some other debt securities to a decline in market value when interest rates rise.</p><p>Adjustable Rate Securities</p><p>Because changes in interest rates on adjustable rate securities may lag behind changes in market rates, the value of such securities may decline during periods of rising interest rates until their interest rates reset to market rates. If the changes in market rates are substantial, the interest rate on an adjustable rate security may not reset during a single adjustment period. Lifetime limits on resets may also prevent their rates from adjusting to market rates.</p><p>During periods of declining interest rates, because the interest rates on adjustable rate securities generally reset downward, their market value is unlikely to rise to the same extent as the value of comparable fixed rate securities.</p><p>Credit</p><p>An issuer of debt securities may fail to make interest payments and repay principal when due, in whole or in part. Changes in an issuer's financial strength or in a security's credit rating may affect a security's value. While securities issued by Ginnie Mae are backed by the full faith and credit of the U.S. government, not all securities of the various U.S. government agencies are, including those of Fannie Mae and Freddie Mac. Also guarantees of principal and interest do not apply to market prices, yields or the Fund&#146;s share price. While the U.S. government has provided financial support to Fannie Mae and Freddie Mac, no assurance can be given that the U.S. government will always do so, since the U.S. government is not so obligated by law. Accordingly, securities issued by Fannie Mae and Freddie Mac may involve a risk of non-payment of principal and interest. Any downgrade of the credit rating of the securities issued by the U.S. government may result in a downgrade of securities issued by its agencies or instrumentalities, including government-sponsored entities.</p><p>Prepayment</p><p>Prepayment risk occurs when a debt security can be repaid in whole or in part prior to the security's maturity and the Fund must reinvest the proceeds it receives, during periods of declining interest rates, in securities that pay a lower rate of interest.</p><p><b>Extension Risk</b></p><p>Some debt securities, particularly mortgage-backed securities, are subject to the risk that the debt security&#146;s effective maturity is extended because calls or prepayments are less or slower than anticipated, particularly when interest rates rise. The market value of such security may then decline and become more interest rate sensitive.</p><p>Income</p><p>Because the Fund can only distribute what it earns, the Fund's distributions to shareholders may decline when prevailing interest rates fall or when the Fund experiences defaults on debt securities it holds.</p><p>Market</p><p>The market values of securities owned by the Fund will go up or down, sometimes rapidly or unpredictably. A security&#146;s market value 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 securities. When there are more sellers than buyers, prices tend to fall. Likewise, when there are more buyers than sellers, prices tend to rise.</p><p>Management</p><p>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.</p></div>falsefalsefalsenonnum:textBlockItemTypenaNarrative Risk Disclosure. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i -Clause instruction false0Risk Narrative [Text Block]22false 2rr_BarChartAndPerformanceTableHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Performancefalsefalsefalsexbrli:stringItemTypestringRisk/Return Bar Chart and Table.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 false0Bar Chart and Performance Table [Heading]23false 2rr_PerformanceNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>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.</p><p>Sales charges are not reflected in the bar chart, and if those charges were included, returns would be less than those shown.</p></div>falsefalsefalsenonnum:textBlockItemTypenaRisk/Return Bar Chart and Table.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 false0Performance Narrative [Text Block]24false 2rr_BarChartHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00CLASS A ANNUAL TOTAL RETURNSfalsefalsefalsexbrli:stringItemTypestringRisk/Return Bar Chart and Table.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 false0Bar Chart [Heading]25false 2rr_BarChartTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/BarChartData column period compact * column rr_ProspectusShareClassAxis compact * row primary compact * row dei_LegalEntityAxis compact fist_S000006850Member ~falsefalseBarChart1.jpg~ http://xbrl.sec.gov/rr/role/BarChartData column period compact * column rr_ProspectusShareClassAxis compact * row primary compact * row dei_LegalEntityAxis compact fist_S000006850Member ~falsehttp://xbrl.sec.gov/rr/role/BarChartData020050 - Schedule - Annual Total Returnstruefalsefalse1falseColumnperiodPeriod*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMemberClass ARatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 USDfalsefalseduration2013-09-20T00:00:002013-09-20T00:00:00$1falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member3false3false 2rr_AnnualReturn2003rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01230.0123falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2003 2rr_AnnualReturn2003rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2003falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2003rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01230.0123falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 20032falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member4false4false 2rr_AnnualReturn2004rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01790.0179falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2004 2rr_AnnualReturn2004rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2004falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2004rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01790.0179falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 20043falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member5false5false 2rr_AnnualReturn2005rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.02060.0206falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2005 2rr_AnnualReturn2005rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2005falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2005rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.02060.0206falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 20054falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member6false6false 2rr_AnnualReturn2006rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04150.0415falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2006 2rr_AnnualReturn2006rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2006falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2006rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04150.0415falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 20065falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member7false7false 2rr_AnnualReturn2007rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.05030.0503falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2007 2rr_AnnualReturn2007rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2007falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2007rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.05030.0503falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 20076falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member8false8false 2rr_AnnualReturn2008rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.03580.0358falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2008 2rr_AnnualReturn2008rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2008falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2008rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.03580.0358falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 20087falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member9false9false 2rr_AnnualReturn2009rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04350.0435falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2009 2rr_AnnualReturn2009rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2009falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2009rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04350.0435falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 20098falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member10false10false 2rr_AnnualReturn2010rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01290.0129falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2010 2rr_AnnualReturn2010rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2010falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2010rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01290.0129falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 20109falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member11false11false 2rr_AnnualReturn2011rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01720.0172falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2011 2rr_AnnualReturn2011rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 2011falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2011rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01720.0172falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 201110falseRowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Member12false12false 2rr_AnnualReturn2012rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01420.0142falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2012 2rr_AnnualReturn2012rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2012falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberFranklin Adjustable U.S. Government Securities Fund 0rr_AnnualReturn2012rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.01420.0142falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 2012falseAnnual Total Returns Franklin Adjustable U.S. Government Securities FundUnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet11009110023ColumnperiodPeriod*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*Rowdei_LegalEntityAxisAxisfist_S000006850Memberfalsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to BarChartData.No definition available.false0Bar Chart [Table]26false 2rr_BarChartClosingTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<table style="font: 11px sans-serif; background-color:#DDDDDD" border="0" cellspacing="0" cellpadding="5" width="745"><tr><td style="border-bottom: 2px solid #ffffff;" valign="top">Best Quarter:</td><td style="border-bottom: 2px solid #ffffff;" valign="bottom" align="right">Q1'09</td><td style="border-bottom: 2px solid #ffffff;" valign="bottom" align="right">1.72%</td></tr><tr><td style="border-bottom: 2px solid #ffffff;" valign="top">Worst Quarter:</td><td style="border-bottom: 2px solid #ffffff;" valign="bottom" align="right">Q4'12</td><td style="border-bottom: 2px solid #ffffff;" valign="bottom" align="right">-0.39%</td></tr><tr><td style="border-bottom: 2px solid #ffffff;" valign="top" colspan="3">As of June 30, 2013, the Fund's year-to-date return was -0.05%.</td></tr></table>falsefalsefalsenonnum:textBlockItemTypenaIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Bar Chart Closing [Text Block]27false 2rr_PerformanceTableHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>AVERAGE ANNUAL TOTAL RETURNS<br/>(figures reflect sales charges)</p><p>For the periods ended December 31, 2012</p></div>falsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit c false0Performance Table Heading28false 2rr_PerformanceTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00~ http://xbrl.sec.gov/rr/role/PerformanceTableData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * column rr_PerformanceMeasureAxis compact * row primary compact * ~falsefalse~ http://xbrl.sec.gov/rr/role/PerformanceTableData column dei_LegalEntityAxis compact fist_S000006850Member column rr_ProspectusShareClassAxis compact * column rr_PerformanceMeasureAxis compact * row primary compact * ~truehttp://xbrl.sec.gov/rr/role/PerformanceTableData020060 - Schedule - Average Annual Total Returns {Transposed}truefalsefalse1falseColumnprimaryElement*3false 2rr_AverageAnnualReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Label USDfalsefalse$2falseColumnprimaryElement*4false 2rr_AverageAnnualReturnYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false01 Year USDfalsefalse$3falseColumnprimaryElement*5false 2rr_AverageAnnualReturnYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false05 Years USDfalsefalse$4falseColumnprimaryElement*6false 2rr_AverageAnnualReturnYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false010 Years USDfalsefalse$1falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMembertruefalseShare Classesrr_ProspectusShareClassAxisrr_ShareClassDomainrr_ProspectusShareClassAxisexplicitMemberfalsefalseBarclays U.S. Government Index: 1-2 Year Componentrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldifist_Index1007Memberrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundShare ClassesBarclays U.S. Government Index: 1-2 Year ComponentRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2truetruetrue0.00370.0037falsefalsefalse3truetruetrue0.02040.0204falsefalsefalse4truetruetrue0.02560.0256falsefalsefalsenanafalse0Barclays U.S. Government Index: 1-2 Year Component2falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMembertruefalseBefore Taxesrr_PerformanceMeasureAxisrr_PerformanceMeasureDomainrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass ABefore TaxesRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsetruefalse00Return Before Taxesfalsefalsefalse2truetruetrue-0.0082-0.0082falsefalsefalse3truetruetrue0.02010.0201falsefalsefalse4truetruetrue0.02420.0242falsefalsefalsenanafalse0Class A3falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMemberfalsefalseAfter Taxes on Distributionsrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldirr_AfterTaxesOnDistributionsMemberrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass AAfter Taxes on DistributionsRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2truetruetrue-0.0135-0.0135falsefalsefalse3truetruetrue0.01110.0111falsefalsefalse4truetruetrue0.01300.0130falsefalsefalsenanafalse0Class A After Taxes on Distributions4falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Arr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018509Memberrr_ProspectusShareClassAxisexplicitMemberfalsefalseAfter Taxes on Distributions and Salesrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldirr_AfterTaxesOnDistributionsAndSalesMemberrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass AAfter Taxes on Distributions and SalesRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2truetruetrue-0.0053-0.0053falsefalsefalse3truetruetrue0.01190.0119falsefalsefalse4truetruetrue0.01400.0140falsefalsefalsenanafalse0Class A After Taxes on Distributions and Sales5falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseClass Crr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000018510Memberrr_ProspectusShareClassAxisexplicitMembertruefalseBefore Taxesrr_PerformanceMeasureAxisrr_PerformanceMeasureDomainrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundClass CBefore TaxesRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2truetruetrue0.00130.0013falsefalsefalse3truetruetrue0.02080.0208falsefalsefalse4truetruetrue0.02270.0227[1]falsefalsefalsenanafalse0Class C6falseRowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*duration2013-09-20T00:00:002013-09-20T00:00:00falsefalseFranklin Adjustable U.S. Government Securities Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldifist_S000006850Memberdei_LegalEntityAxisexplicitMemberfalsefalseAdvisor Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldifist_C000064441Memberrr_ProspectusShareClassAxisexplicitMembertruefalseBefore Taxesrr_PerformanceMeasureAxisrr_PerformanceMeasureDomainrr_PerformanceMeasureAxisexplicitMemberFranklin Adjustable U.S. Government Securities FundAdvisor ClassBefore TaxesRatioStandardhttp://www.xbrl.org/2003/instancepurexbrli0Standard0 0truefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2truetruetrue0.01680.0168falsefalsefalse3truetruetrue0.02720.0272falsefalsefalse4truetruetrue0.02780.0278[2]falsefalsefalsenanafalse0Advisor Class1Since inception July 1, 2003.2Since inception May 15, 2008.falseAverage Annual Total Returns Franklin Adjustable U.S. Government Securities FundUnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet46182046076ColumnprimaryElement*RowperiodPeriod*Rowdei_LegalEntityAxisAxisfist_S000006850MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to PerformanceTableData.No definition available.false0Performance [Table]29false 2rr_PerformanceTableClosingTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div><p>Performance information for Class R6 shares is not shown because it had not commenced operations as of the date of this prospectus.</p><p>Historical performance for Advisor Class shares prior to their inception is based on the performance of Class A shares. Advisor Class performance has been adjusted to reflect differences in sales charges between classes.</p><p>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.</p></div>falsefalsefalsenonnum:textBlockItemTypenaIf the Fund has annual returns for at least one calendar year, provide a table showing the Fund's (A) average annual total return; (B) average annual total return (after taxes on distributions); and (C) average annual total return (after taxes on distributions and redemption). A Money Market Fund should show only the returns described in clause (A) of the preceding sentence. All returns should be shown for 1-, 5-, and 10- calendar year periods ending on the date of the most recently completed calendar year (or for the life of the Fund, if shorter), but only for periods subsequent to the effective date of the Fund's registration statement. The table also should show the returns of an appropriate broad-based securities market index as defined in Instruction 5 to Item 22(b)(7) for the same periods. A Fund that has been in existence for more than 10 years also may include returns for the life of the Fund. A Money Market Fund may provide the Fund's 7-day yield ending on the date of the most recent calendar year or disclose a toll-free (or collect) telephone number that investors can use to obtain the Fund's current 7-day yield. For a Fund (other than a Money Market Fund or a Fund described in General Instruction C.3.(d)(iii)), provide the information in the following table with the specified captions AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, _____)Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii false0Performance Table Closing [Text Block]falseRisk/Return SummaryUnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://xbrl.sec.gov/rr/role/RiskReturn129