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rr_RiskReturnAbstract

Document Type

dei_DocumentType

485BPOS

Document Period End Date

dei_DocumentPeriodEndDate

Sep. 30, 2012

Registrant Name

dei_EntityRegistrantName

FRANKLIN STRATEGIC MORTGAGE PORTFOLIO

Central Index Key

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0000893226

Amendment Flag

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false

Document Creation Date

dei_DocumentCreationDate

Jan. 28, 2013

Document Effective Date

dei_DocumentEffectiveDate

Feb. 01, 2013

Prospectus Date

rr_ProspectusDate

Feb. 01, 2013

Risk/Return [Heading]

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Fund Summary

Franklin Strategic Mortgage Portfolio

Objective, Primary [Text Block]

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Objective [Heading]

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Investment Goal

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High total return (a combination of high current income and capital appreciation) relative to the performance of the general mortgage securities market.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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These tables describe the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts in Class A if you and your family invest, or agree to invest in the future, at least $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 34 in the Fund's Prospectus and under “Buying and Selling Shares” on page 53 of the Fund’s Statement of Additional Information.

Shareholder Fees Caption [Text]

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SHAREHOLDER FEES (fees paid directly from your investment)

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES

(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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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 594.80% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

594.80%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts in Class A if you and your family invest, or agree to invest in the future, at least $100,000 in Franklin Templeton funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

100,000

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of the period. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example reflects adjustments made to the Fund's operating expenses due to the fee waiver and/or expense reimbursement by the investment manager and/or administrator for the 1 Year numbers only. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If you do not sell your shares:

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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Under normal market conditions, the Fund invests at least 80% of its net assets in mortgage securities. The Fund invests substantially in mortgage securities that are issued or guaranteed by the U.S. government, its agencies or instrumentalities, which include mortgage pass-through securities representing interests in "pools" of mortgage loans issued or guaranteed by the Government National Mortgage Association (Ginnie Mae), Fannie Mae, and Freddie Mac. These securities may be fixed-rate or adjustable-rate mortgage securities (ARMS). Government agency or instrumentality issues have different levels of credit support.

The Fund also invests in other types of mortgage securities including, but not limited to, certain ARMS, commercial mortgage-backed securities (CMBS), home equity loan asset-backed securities (HELs), manufactured housing asset-backed securities (MHs), and collateralized mortgage obligations (CMOs), as well as in other mortgage-related asset-backed securities. The Fund also may invest in U.S. Treasury securities. The Fund may invest a small portion of its assets directly in mortgage loans.

The Fund may invest up to 15% of its assets in foreign securities, which may include non-U.S. dollar denominated foreign mortgage securities. In addition, the Fund may invest up to 20% of its total assets in high-yield, lower-quality securities rated, at the time of purchase, below BBB by S&P®, or Baa by Moody’s, respectively, or, if unrated, deemed to be of comparable quality by the investment manager. The Fund may also invest up to 33% of its gross assets in mortgage dollar rolls and may buy securities on a "when-issued" or "delayed delivery" basis.

For purposes of pursuing its investment goal, the Fund may enter into interest rate and credit related transactions involving certain derivative instruments, including interest rate and credit default swaps and U.S. Treasury futures contracts. The Fund may use these derivative instruments for hedging purposes or for other investment purposes, including to generate income, to increase liquidity and/or to gain exposure to certain instruments or markets in a more efficient or less expensive way. The use of credit default swaps may allow the Fund to obtain net long or short exposure to select credit risks. The Fund may also enter into currency-related derivative transactions, including currency forwards and currency swaps.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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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.

Interest Rate

When interest rates rise, debt security prices generally fall. The opposite is also generally true: debt security prices rise when interest rates fall. In general, securities with longer maturities are more sensitive to these interest rate changes.

Prepayment

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.

Mortgage-Backed Securities and Prepayment

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.

Asset-Backed Securities

Issuers of asset-backed securities may have limited ability to enforce the security interest in the underlying assets, and credit enhancements provided to support the securities, if any, may be inadequate to protect investors in the event of default. Like mortgage-backed securities, asset-backed securities are subject to prepayment and extension risks.

Credit

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 or government's credit rating may affect a security's value. Mortgage-backed securities that are not issued by U.S. government agencies may have a greater risk of default because neither of the U.S. government nor an agency or instrumentality have guaranteed them. The credit quality of most asset-backed securities depends primarily on the credit quality of the underlying assets and the amount of credit support (if any) provided to the securities. 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’s share price. While the U.S. government has recently 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.

Foreign Securities

Investing in foreign securities typically involves more risks than investing in U.S. securities, including risks related to currency exchange rates and policies, country or government specific issues, less favorable trading practices or regulation and greater price volatility. Certain of these risks also may apply to securities of U.S. companies with significant foreign operations.

Income

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.

High-Yield Mortgage Securities

Mortgage securities that are rated below investment grade, or unrated and deemed to be of comparable quality by the investment manager, involve greater credit risk with respect to the issuers of the mortgage securities and the borrowers in the underlying mortgages than higher-quality mortgage securities. High-yield mortgage securities are more vulnerable to changes in the relevant economy, such as a recession or a sustained period of rising interest rates. The prices of high-yield mortgage securities generally fluctuate more than those of higher credit quality and are generally more illiquid (harder to sell) and harder to value.

Market

The market values of securities owned by the Fund will go up or down, sometimes rapidly or unpredictably. A security’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.

Management

The Fund is subject to management risk because it is an actively managed investment portfolio. The Fund's investment manager applies investment techniques and risk analyses in making investment decisions for the Fund, but there can be no guarantee that these decisions will produce the desired results.

Mortgage Dollar Rolls

In a mortgage dollar roll, the Fund takes the risk that: the market price of the mortgage-backed securities will drop below their future purchase price; the securities that it repurchases at a later date will have less favorable market characteristics; the other party to the agreement will not be able to perform; the roll adds leverage to the Fund's portfolio; and, it increases the Fund's sensitivity to interest rate changes. In addition, investment in mortgage dollar rolls may increase the turnover rate for the Fund.

Derivative Instruments

The performance of derivative instruments (including currency-related derivatives) depends largely on the performance of an underlying currency, security or index, and such instruments often have risks similar to their underlying instrument, in addition to other risks. Derivatives involve costs and can create economic leverage in the Fund's portfolio which may result in significant volatility and cause the Fund to participate in losses (as well as gains) in an amount that significantly exceeds the Fund's initial investment. Other risks include illiquidity, mispricing or improper valuation of the derivative instrument, and imperfect correlation between the value of the derivative and the underlying instrument so that the Fund may not realize the intended benefits. When used for hedging, the change in value of the derivative may also not correlate specifically with the currency, security or other risk being hedged. With over-the-counter derivatives, there is the risk that the other party to the transaction will fail to perform.

When-Issued and Delayed Delivery Transactions

Mortgage-backed securities may be issued on a when-issued or delayed delivery basis, where payment and delivery take place at a future date. Since the market price of the security may fluctuate during the time before payment and delivery, the Fund assumes the risk that the value of the security at delivery may be more or less than the purchase price.

Bar Chart and Performance Table [Heading]

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Performance

Performance Narrative [Text Block]

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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.

Sales charges are not reflected in the bar chart, and if those charges were included, returns would be less than those shown.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Phone [Text]

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(800) DIAL BEN/342-5236

Performance Availability Website Address [Text]

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franklintempleton.com

Performance Past Does Not Indicate Future [Text]

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The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Bar Chart [Heading]

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CLASS A ANNUAL TOTAL RETURNS

^[1]

Bar Chart Does Not Reflect Sales Loads [Text]

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Sales charges are not reflected in the bar chart, and if those charges were included, returns would be less than those shown.

Bar Chart Closing [Text Block]

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Best Quarter:	Q3'09	4.47%
Worst Quarter:	Q4'08	-3.64%

Performance Table Heading

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AVERAGE ANNUAL TOTAL RETURNS
(figures reflect sales charges)

For the periods ended December 31, 2012

Performance Table Closing [Text Block]

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Historical performance for Class A, Class C and Advisor Class shares prior to their inception is based on the performance of Class A1 shares. This performance has been adjusted to reflect differences in sales charges and/or Rule 12b-1 fees, as applicable.

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.

Franklin Strategic Mortgage Portfolio | Citigroup U.S. Broad Investment-Grade (USBIG) Mortgage Index

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

2.60%

rr_AverageAnnualReturnYear05

5.73%

rr_AverageAnnualReturnYear10

5.13%

Franklin Strategic Mortgage Portfolio | Class A

Maximum Cumulative Sales Charge (as a percentage of Offering Price)

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4.25%

Maximum Deferred Sales Charge (as a percentage of Offering Price)

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none

rr_ManagementFeesOverAssets

0.40%

rr_DistributionAndService12b1FeesOverAssets

0.25%

rr_OtherExpensesOverAssets

0.37%

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

rr_ExpensesOverAssets

1.03%

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[2]

rr_NetExpensesOverAssets

1.02%

^[3]

rr_ExpenseExampleYear01

525

rr_ExpenseExampleYear03

738

rr_ExpenseExampleYear05

969

Highest Quarterly Return, Label

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1,631

Annual Return 2003

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2.42%

Annual Return 2004

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4.24%

Annual Return 2005

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1.93%

Annual Return 2006

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4.22%

Annual Return 2007

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4.01%

Annual Return 2008

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(6.74%)

Annual Return 2009

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10.34%

Annual Return 2010

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10.97%

Annual Return 2011

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6.61%

Annual Return 2012

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5.81%

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Best Quarter:

Highest Quarterly Return, Date

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Sep. 30, 2009

Highest Quarterly Return

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4.47%

Lowest Quarterly Return, Label

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Worst Quarter:

Lowest Quarterly Return, Date

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Dec. 31, 2008

Lowest Quarterly Return

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(3.64%)

Label

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Return Before Taxes

rr_AverageAnnualReturnYear01

1.28%

rr_AverageAnnualReturnYear05

4.30%

rr_AverageAnnualReturnYear10

3.82%

Franklin Strategic Mortgage Portfolio | Class A | After Taxes on Distributions

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rr_AverageAnnualReturnYear01

0.11%

rr_AverageAnnualReturnYear05

2.51%

rr_AverageAnnualReturnYear10

2.00%

Franklin Strategic Mortgage Portfolio | Class A | After Taxes on Distributions and Sales

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rr_AverageAnnualReturnYear01

0.82%

rr_AverageAnnualReturnYear05

2.58%

rr_AverageAnnualReturnYear10

2.14%

Franklin Strategic Mortgage Portfolio | Class A1

Maximum Cumulative Sales Charge (as a percentage of Offering Price)

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rr_MaximumCumulativeSalesChargeOverOfferingPrice

4.25%

Maximum Deferred Sales Charge (as a percentage of Offering Price)

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none

rr_ManagementFeesOverAssets

0.40%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.37%

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

rr_ExpensesOverAssets

0.78%

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[2]

rr_NetExpensesOverAssets

0.77%

^[3]

rr_ExpenseExampleYear01

500

rr_ExpenseExampleYear03

663

rr_ExpenseExampleYear05

839

rr_ExpenseExampleYear10

1,349

rr_AverageAnnualReturnYear01

1.53%

rr_AverageAnnualReturnYear05

4.58%

rr_AverageAnnualReturnYear10

4.14%

Franklin Strategic Mortgage Portfolio | Class C

Maximum Cumulative Sales Charge (as a percentage of Offering Price)

rr_RiskReturnAbstract

rr_MaximumCumulativeSalesChargeOverOfferingPrice

none

Maximum Deferred Sales Charge (as a percentage of Offering Price)

rr_MaximumDeferredSalesChargeOverOfferingPrice

1.00%

rr_ManagementFeesOverAssets

0.40%

rr_DistributionAndService12b1FeesOverAssets

0.65%

rr_OtherExpensesOverAssets

0.37%

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

rr_ExpensesOverAssets

1.43%

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[2]

rr_NetExpensesOverAssets

1.42%

^[3]

rr_ExpenseExampleYear01

245

rr_ExpenseExampleYear03

451

rr_ExpenseExampleYear05

781

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleYear10

1,713

rr_ExpenseExampleNoRedemptionYear01

145

Expense Example, No Redemption, 3 Years

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451

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

781

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

1,713

rr_AverageAnnualReturnYear01

4.31%

rr_AverageAnnualReturnYear05

4.75%

rr_AverageAnnualReturnYear10

3.78%

Franklin Strategic Mortgage Portfolio | Advisor Class

Maximum Cumulative Sales Charge (as a percentage of Offering Price)

rr_RiskReturnAbstract

rr_MaximumCumulativeSalesChargeOverOfferingPrice

none

Maximum Deferred Sales Charge (as a percentage of Offering Price)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.40%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.37%

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

rr_ExpensesOverAssets

0.78%

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[2]

rr_NetExpensesOverAssets

0.77%

^[3]

rr_ExpenseExampleYear01

rr_ExpenseExampleYear03

248

rr_ExpenseExampleYear05

432

rr_ExpenseExampleYear10

966

rr_AverageAnnualReturnYear01

6.05%

rr_AverageAnnualReturnYear05

5.49%