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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY INCOME FUND /MA/
Prospectus Date rr_ProspectusDate Sep. 28, 2013
Inst | Fidelity Income Replacement 2042 Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary

Fund/Class:
Fidelity Income Replacement 2042 FundSM/Fidelity Advisor Income Replacement 2042 FundSM Institutional
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The fund seeks total return through a combination of current income and capital growth.
Expense [Heading] rr_ExpenseHeading Fee Table
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees
(fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual class operating expenses
(expenses that you pay each year as a % of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund will not incur transaction costs, such as commissions, when it buys and sells shares of underlying Fidelity funds (or "turns over" its portfolio), but it could incur transaction costs if it were to buy and sell other types of securities directly. If the fund were to buy and sell other types of securities directly, a higher portfolio turnover rate could indicate higher transaction costs and could result in higher taxes when fund shares are held in a taxable account. Such costs, if incurred, would not be reflected in annual operating expenses or in the example and would affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 34% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.00%
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees Differs from the ratios of expenses to average net assets in the Financial Highlights section of the prospectus because of acquired fund fees and expenses.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This example helps compare the cost of investing in the fund with the cost of investing in other funds. The example assumes that you are not participating in the Smart Payment Program®.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
  • Investing in a combination of underlying Fidelity equity funds, bond funds, and short-term funds using an asset allocation strategy designed to achieve a level of total return consistent with a payment strategy to be administered through the fund's horizon date, December 31, 2042.
  • Allocating assets among underlying Fidelity funds according to an asset allocation strategy that begins with a relatively more aggressive asset allocation and gradually shifts to a relatively more conservative asset allocation over the fund's time horizon.
  • Using an asset allocation among underlying Fidelity funds as of July 31, 2013, of approximately:
  
Equity Funds  
  Domestic Equity Funds 50.0%
  International Equity Fund 12.3%
  
Bond Funds 
  Investment-Grade Bond Funds 26.1%
  High Yield Bond Funds 6.4%
  
Short-Term Funds 
  Short-Term Funds5.2%

The payment strategy is designed to be implemented through a shareholder's voluntary participation in the Smart Payment Program®. The Smart Payment Program is an optional account feature designed, but not guaranteed, to enable shareholders to receive from the fund monthly payments that have the potential to keep pace with inflation over the fund's time horizon. The fund's investment objective is intended to support the Smart Payment Program's payment strategy. However, shareholders may invest in the fund and not participate in the Smart Payment Program. Investors should refer to the Features and Policies section of the prospectus for a summary of how the Smart Payment Program works.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
  • The fund is not designed for the accumulation of assets prior to retirement. The fund does not provide a complete solution for a shareholder's retirement income needs.
  • If you participate in the Smart Payment Program, your entire investment in the fund will be gradually liquidated over time.
  • If Strategic Advisers' asset allocation strategy does not work as intended, the fund may not achieve its objective. If the fund is unable to achieve its objective, the Smart Payment Program's payment strategy may not work as intended, which could mean that monthly payments would not keep pace with inflation.
  • Investing in Other Funds. The fund bears all risks of investment strategies employed by the underlying funds, including the risk that the underlying funds will not meet their investment objectives.
  • Stock Market Volatility. Stock markets are volatile and can decline significantly in response to adverse issuer, political, regulatory, market, or economic developments. Different parts of the market, including different market sectors, and different types of securities can react differently to these developments.
  • Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
  • Foreign Exposure. Foreign markets, particularly emerging markets, can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market. Emerging markets can be subject to greater social, economic, regulatory, and political uncertainties and can be extremely volatile. Foreign exchange rates also can be extremely volatile.
  • Industry Exposure. Market conditions, interest rates, and economic, regulatory, or financial developments could significantly affect a single industry or group of related industries.
  • Prepayment. The ability of an issuer of a debt security to repay principal prior to a security's maturity can cause greater price volatility if interest rates change.
  • Issuer-Specific Changes. The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a security to decrease. Lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities) and certain types of other securities involve greater risk of default or price changes due to changes in the credit quality of the issuer. The value of lower-quality debt securities and certain types of other securities can be more volatile due to increased sensitivity to adverse issuer, political, regulatory, market, or economic developments and can be difficult to resell.
  • Leverage Risk. Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly.
  • "Value" Investing. "Value" stocks can perform differently from the market as a whole and other types of stocks and can continue to be undervalued by the market for long periods of time.
An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You could lose money by investing in the fund.
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time. The index description appears in the Additional Index Information section of the prospectus. Past performance (before and after taxes) is not an indication of future performance.

Visit www.advisor.fidelity.com for updated return information.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.advisor.fidelity.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Returns
Calendar Years
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown in the chart:
Returns
Quarter ended
Highest Quarter Return
15.68%
June 30, 2009
Lowest Quarter Return
-16.58%
December 31, 2008
Year-to-Date Return
6.66%
June 30, 2013
Performance Table Heading rr_PerformanceTableHeading Average Annual Returns
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes. Actual after-tax returns may differ depending on your individual circumstances. The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement.

For the periods ended
December 31, 2012
Inst | Fidelity Income Replacement 2042 Fund | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets none
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total annual operating expenses rr_ExpensesOverAssets 0.67% [1]
1 year rr_ExpenseExampleYear01 68
3 years rr_ExpenseExampleYear03 214
5 years rr_ExpenseExampleYear05 373
10 years rr_ExpenseExampleYear10 $ 835
2008 rr_AnnualReturn2008 (30.02%)
2009 rr_AnnualReturn2009 28.91%
2010 rr_AnnualReturn2010 13.75%
2011 rr_AnnualReturn2011 (2.10%)
2012 rr_AnnualReturn2012 13.78%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-Date Return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 6.66%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.68%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (16.58%)
Inst | Fidelity Income Replacement 2042 Fund | Return Before Taxes | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return Before Taxes
Past 1 year rr_AverageAnnualReturnYear01 13.78%
Past 5 years rr_AverageAnnualReturnYear05 2.71%
Life of class rr_AverageAnnualReturnSinceInception 2.71% [2]
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2007
Inst | Fidelity Income Replacement 2042 Fund | Return After Taxes on Distributions | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
Past 1 year rr_AverageAnnualReturnYear01 13.04%
Past 5 years rr_AverageAnnualReturnYear05 1.97%
Life of class rr_AverageAnnualReturnSinceInception 1.97% [2]
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2007
Inst | Fidelity Income Replacement 2042 Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
Past 1 year rr_AverageAnnualReturnYear01 9.24%
Past 5 years rr_AverageAnnualReturnYear05 1.92%
Life of class rr_AverageAnnualReturnSinceInception 1.92% [2]
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2007
Inst | Fidelity Income Replacement 2042 Fund | S&P 500® Index (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel S&P 500® Index
Past 1 year rr_AverageAnnualReturnYear01 16.00%
Past 5 years rr_AverageAnnualReturnYear05 1.66%
Life of class rr_AverageAnnualReturnSinceInception 1.66% [2]
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2007
[1] Differs from the ratios of expenses to average net assets in the Financial Highlights section of the prospectus because of acquired fund fees and expenses.
[2] From December 31, 2007.