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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY HASTINGS STREET TRUST
Prospectus Date rr_ProspectusDate Aug. 09, 2013
Z | Fidelity Mega Cap Stock Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary

Fund/Class:
Fidelity® Mega Cap Stock Fund/Fidelity Advisor® Mega Cap Stock Fund Z
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The fund seeks high total return through a combination of current income and 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 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 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 operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 57% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 57.00%
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
  • Normally investing at least 80% of assets in common stocks of companies with mega market capitalizations (which, for purposes of this fund, are those companies with market capitalizations similar to companies in the Russell Top 200® Index or the S&P 100® Index).
  • Investing in domestic and foreign issuers.
  • Investing in either "growth" stocks or "value" stocks or both.
  • Using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
  • 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.
  • Foreign Exposure. Foreign 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.
  • 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.
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 and an additional index over various periods of time. The indexes have characteristics relevant to the fund's investment strategies. Index descriptions appear in the Additional Index Information section of the prospectus. Past performance is not an indication of future performance.

Visit www.advisor.fidelity.com for updated return information.

Performance history will be available for Class Z after Class Z has been in operation for one calendar year.
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 and an additional 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 is not an indication of future performance.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Returns
Calendar Years		 [1]
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown in the chart:
Returns
Quarter ended
Highest Quarter Return
18.36%
June 30, 2009
Lowest Quarter Return
-13.08%
September 30, 2011
Year-to-Date Return
14.25%
June 30, 2013
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The returns shown above are for Institutional Class, which is not offered through this prospectus. Class Z would have substantially similar annual returns to Institutional Class because the classes are invested in the same portfolio of securities. Class Z's returns would differ from Institutional Class's returns to the extent that the classes do not have the same expenses.
Performance Table Heading rr_PerformanceTableHeading Average Annual Returns
For the periods ended
December 31, 2012
Z | Fidelity Mega Cap Stock Fund | Class Z
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management fee rr_ManagementFeesOverAssets 0.46%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.11% [2]
Total annual operating expenses rr_ExpensesOverAssets 0.57%
1 year rr_ExpenseExampleYear01 58
3 years rr_ExpenseExampleYear03 183
5 years rr_ExpenseExampleYear05 318
10 years rr_ExpenseExampleYear10 $ 714
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Performance history will be available for Class Z after Class Z has been in operation for one calendar year.
Z | Fidelity Mega Cap Stock Fund | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
2009 rr_AnnualReturn2009 28.55% [1]
2010 rr_AnnualReturn2010 14.35% [1]
2011 rr_AnnualReturn2011 2.28% [1]
2012 rr_AnnualReturn2012 19.48% [1]
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 14.25%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.36%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.08%)
Label rr_AverageAnnualReturnLabel Institutional Class
Past 1 year rr_AverageAnnualReturnYear01 19.48% [1]
Life of class rr_AverageAnnualReturnSinceInception 3.75% [1],[3]
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 05, 2008
Z | Fidelity Mega Cap Stock 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%
Life of class rr_AverageAnnualReturnSinceInception 3.63% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 05, 2008
Z | Fidelity Mega Cap Stock Fund | Russell Top 200® Index (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Russell Top 200® Index
Past 1 year rr_AverageAnnualReturnYear01 16.04%
Life of class rr_AverageAnnualReturnSinceInception 3.24% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 05, 2008
[1] The returns shown above are for Institutional Class, which is not offered through this prospectus. Class Z would have substantially similar annual returns to Institutional Class because the classes are invested in the same portfolio of securities. Class Z's returns would differ from Institutional Class's returns to the extent that the classes do not have the same expenses.
[2] Based on estimated amounts for the current fiscal year.
[3] From February 5, 2008.