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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY ABERDEEN STREET TRUST
Prospectus Date rr_ProspectusDate Jul. 30, 2014
Retail | Fidelity Freedom Index 2060 Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary

Fund/Class:
FidelityFreedom®Index 2060 Fund/Fidelity Freedom Index 2060 Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The fund seeks high total return until its target retirement date. Thereafter the fund's objective will be to seek high current income and, as a secondary objective, capital appreciation.
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 operating expenses
(expenses that you pay each year as a % of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2017
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.
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Based on estimated amounts for the current fiscal year.
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.

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
  • Strategic Advisers, Inc. (Strategic Advisers) may continue to seek high total return for several years beyond the fund's target retirement date in an effort to achieve the fund's overall investment objective.
  • Investing in a combination of underlying Fidelity funds, each of which (excluding the money market fund) seeks to provide investment results that correspond to the total return of a specific index or market segment.
  • Allocating assets among underlying Fidelity funds according to an asset allocation strategy that becomes increasingly conservative until it reaches approximately 17% in domestic equity funds (including commodity funds), 7% in international equity funds, 46% in bond funds (including treasury inflation-protected security funds), and 30% in short-term funds (approximately 10 to 19 years after the year 2060).
  • Using an asset allocation among underlying Fidelity funds as of inception of approximately:
  
Domestic Equity Funds  
  Domestic Equity Fund 61.6%
  Commodity Fund 1.4%
  
International Equity Funds 
  International Equity Fund27.0%
  
Bond Funds 
  Investment-Grade Bond Fund 10.0%
  Inflation-Protected Bond Fund 0.0%
  
Short-Term Funds 
  Short-Term Fund0.0%
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
  • 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.
  • Subsidiary Risk. Investment in an unregistered subsidiary is not subject to the investor protections of the Investment Company Act of 1940 (1940 Act) and is subject to the risks associated with investing in derivatives and commodity-linked investing in general. Changes in tax and other laws could negatively affect investments in the subsidiary.
  • 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.
  • Correlation to Index. The performance of an underlying index fund and its index may vary somewhat due to factors such as transaction costs, sample selection, and timing differences associated with additions to and deletions from the index.
  • Leverage Risk. Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly.
  • Commodity-Linked Investing. The value of commodities and commodity-linked investments may be affected by the performance of the overall commodities markets as well as weather, political, tax, and other regulatory and market developments. Commodity-linked investments may be more volatile and less liquid than the underlying commodity, instruments, or measures.
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 One Year or Less [Text] rr_PerformanceOneYearOrLess Performance history will be available for the fund after the fund has been in operation for one calendar year.
Retail | Fidelity Freedom Index 2060 Fund | Class: Fidelity Freedom Index 2060 Fund
  
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 0.15% [1]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.09% [1]
Total annual operating expenses rr_ExpensesOverAssets 0.24%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.08% [2]
Total annual operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.16%
1 year rr_ExpenseExampleYear01 16
3 years rr_ExpenseExampleYear03 $ 53
[1] Based on estimated amounts for the current fiscal year.
[2] Fidelity Management & Research Company (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (including acquired fund fees and expenses, but excluding interest, certain taxes, certain securities lending costs, brokerage commissions, and extraordinary expenses, if any, incurred by the fund or an acquired fund in which the fund invests) exceed 0.16% of its average net assets. This arrangement will remain in effect through May 31, 2017. FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees.