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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY HASTINGS STREET TRUST
Prospectus Date rr_ProspectusDate Aug. 29, 2020
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <p style="font: bold 20pt Arial, Helvetica, sans-serif;">Fund Summary</p><p style="font: normal 12pt Arial, Helvetica, sans-serif;"><b>Fund/Class</b>:<br/><b>Fidelity® Mega Cap Stock Fund</b>/Fidelity Advisor® Mega Cap Stock Fund A, M, C, I, Z</p>
Objective [Heading] rr_ObjectiveHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;">Investment Objective</font>
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 <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Fee Table</b></font>
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. In addition to the fees and expenses described below, your broker may also require you to pay brokerage commissions on purchases and sales of certain share classes 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 $50,000 in the fund or certain other Fidelity® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 27 of the prospectus. Different intermediaries may provide additional waivers or reductions of the sales charge. Please see “Sales Charge Waiver Policies Applied by Certain Intermediaries” in the “Appendix” section of the prospectus.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <p style="font: bold 11pt Arial, sans-serif; margin-bottom: 0px;">Shareholder fees</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">(fees paid directly from your investment)</p>
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <p style="font: bold 11pt Arial, sans-serif; margin-bottom: 0px;">Annual Operating Expenses</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">(expenses that you pay each year as a % of the value of your investment)</p>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Portfolio Turnover</b></font>
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 49% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 49.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts <font style="FONT-FAMILY: Times New Roman" size="3">You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund or certain other Fidelity® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 27 of the prospectus.</font>
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
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 and if you hold your shares:

Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption <p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">Sell All Shares</p>
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption <p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">Hold Shares</p>
Strategy [Heading] rr_StrategyHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Principal Investment Strategies</b></font>
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 <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Principal Investment Risks</b></font>
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 <font style="FONT-FAMILY: Times New Roman" size="3">You could lose money by investing in the fund.</font>
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution <font style="FONT-FAMILY: Times New Roman" size="3">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.</font>
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Performance</b></font>
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 (before and after taxes) is not an indication of future performance.

Visit institutional.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns <font style="FONT-FAMILY: Times New Roman" size="3">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.</font>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <font style="FONT-FAMILY: Times New Roman" size="3">institutional.fidelity.com</font>
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture <font style="FONT-FAMILY: Times New Roman" size="3">Past performance (before and after taxes) is not an indication of future performance.</font>
Bar Chart [Heading] rr_BarChartHeading <p style="font:bold 11pt Arial, sans-serif; margin-bottom: 0px;">Year-by-Year Returns</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">Calendar Years</p>
Bar Chart Narrative [Text Block] rr_BarChartNarrativeTextBlock

The returns in the bar chart do not reflect any applicable sales charges; if sales charges were reflected, returns would be lower than those shown.
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads <font style="FONT-FAMILY: Times New Roman" size="3">The returns in the bar chart do not reflect any applicable sales charges; if sales charges were reflected, returns would be lower than those shown.</font>
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown in the chart for Class A:ReturnsQuarter ended
Highest Quarter Return14.73%March 31, 2012
Lowest Quarter Return-14.13%December 31, 2018
Year-to-Date Return-9.67%June 30, 2020
Performance Table Heading rr_PerformanceTableHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Average Annual Returns</b></font>
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads <font style="FONT-FAMILY: Times New Roman" size="3">Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges.</font>
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate <font style="FONT-FAMILY: Times New Roman" size="3">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.</font>
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred <font style="FONT-FAMILY: Times New Roman" size="3">The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).</font>
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown <font style="FONT-FAMILY: Times New Roman" size="3">After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary.</font>
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher <font style="FONT-FAMILY: Times New Roman" size="3">Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.</font>
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges. 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. After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary. 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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan). Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.

For the periods ended December 31, 2019
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Fidelity Mega Cap Stock Fund-Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) on purchases (as a % of offering price) rr_MaximumCumulativeSalesChargeOverOfferingPrice 5.75%
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Management fee rr_ManagementFeesOverAssets 0.43%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.25%
Total annual operating expenses rr_ExpensesOverAssets 0.93%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.
1 year rr_ExpenseExampleYear01 $ 664
3 years rr_ExpenseExampleYear03 854
5 years rr_ExpenseExampleYear05 1,060
10 years rr_ExpenseExampleYear10 1,652
1 Year rr_ExpenseExampleNoRedemptionYear01 664
3 Years rr_ExpenseExampleNoRedemptionYear03 854
5 Years rr_ExpenseExampleNoRedemptionYear05 1,060
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,652
2010 rr_AnnualReturn2010 14.10%
2011 rr_AnnualReturn2011 1.97%
2012 rr_AnnualReturn2012 19.18%
2013 rr_AnnualReturn2013 32.89%
2014 rr_AnnualReturn2014 11.23%
2015 rr_AnnualReturn2015 (1.74%)
2016 rr_AnnualReturn2016 13.33%
2017 rr_AnnualReturn2017 17.49%
2018 rr_AnnualReturn2018 (7.47%)
2019 rr_AnnualReturn2019 30.81%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-Date Return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2020
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (9.67%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.73%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (14.13%)
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Fidelity Mega Cap Stock Fund-Class M  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) on purchases (as a % of offering price) rr_MaximumCumulativeSalesChargeOverOfferingPrice 3.50%
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Management fee rr_ManagementFeesOverAssets 0.43%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.25%
Total annual operating expenses rr_ExpensesOverAssets 1.18%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.
1 year rr_ExpenseExampleYear01 $ 466
3 years rr_ExpenseExampleYear03 712
5 years rr_ExpenseExampleYear05 976
10 years rr_ExpenseExampleYear10 1,732
1 Year rr_ExpenseExampleNoRedemptionYear01 466
3 Years rr_ExpenseExampleNoRedemptionYear03 712
5 Years rr_ExpenseExampleNoRedemptionYear05 976
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,732
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Fidelity Mega Cap Stock Fund-Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) on purchases (as a % of offering price) rr_MaximumCumulativeSalesChargeOverOfferingPrice none
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther 1.00% [2]
Management fee rr_ManagementFeesOverAssets 0.43%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual operating expenses rr_ExpensesOverAssets 1.69%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock On Class C shares redeemed less than one year after purchase.
1 year rr_ExpenseExampleYear01 $ 272
3 years rr_ExpenseExampleYear03 533
5 years rr_ExpenseExampleYear05 918
10 years rr_ExpenseExampleYear10 1,998
1 Year rr_ExpenseExampleNoRedemptionYear01 172
3 Years rr_ExpenseExampleNoRedemptionYear03 533
5 Years rr_ExpenseExampleNoRedemptionYear05 918
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,998
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Fidelity Mega Cap Stock Fund- Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) on purchases (as a % of offering price) rr_MaximumCumulativeSalesChargeOverOfferingPrice none
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Management fee rr_ManagementFeesOverAssets 0.43%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual operating expenses rr_ExpensesOverAssets 0.66%
1 year rr_ExpenseExampleYear01 $ 67
3 years rr_ExpenseExampleYear03 211
5 years rr_ExpenseExampleYear05 368
10 years rr_ExpenseExampleYear10 822
1 Year rr_ExpenseExampleNoRedemptionYear01 67
3 Years rr_ExpenseExampleNoRedemptionYear03 211
5 Years rr_ExpenseExampleNoRedemptionYear05 368
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 822
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Fidelity Mega Cap Stock Fund-Class Z  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) on purchases (as a % of offering price) rr_MaximumCumulativeSalesChargeOverOfferingPrice none
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Management fee rr_ManagementFeesOverAssets 0.43%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.10%
Total annual operating expenses rr_ExpensesOverAssets 0.53%
1 year rr_ExpenseExampleYear01 $ 54
3 years rr_ExpenseExampleYear03 170
5 years rr_ExpenseExampleYear05 296
10 years rr_ExpenseExampleYear10 665
1 Year rr_ExpenseExampleNoRedemptionYear01 54
3 Years rr_ExpenseExampleNoRedemptionYear03 170
5 Years rr_ExpenseExampleNoRedemptionYear05 296
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 665
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Return Before Taxes | Fidelity Mega Cap Stock Fund-Class A  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Class A - Return Before Taxes</b></font>
Past 1 year rr_AverageAnnualReturnYear01 23.29%
Past 5 years rr_AverageAnnualReturnYear05 8.34%
Past 10 years rr_AverageAnnualReturnYear10 11.83%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Return Before Taxes | Fidelity Mega Cap Stock Fund-Class M  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Class M - Return Before Taxes</b></font>
Past 1 year rr_AverageAnnualReturnYear01 25.97%
Past 5 years rr_AverageAnnualReturnYear05 8.58%
Past 10 years rr_AverageAnnualReturnYear10 11.81%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Return Before Taxes | Fidelity Mega Cap Stock Fund-Class C  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Class C - Return Before Taxes</b></font>
Past 1 year rr_AverageAnnualReturnYear01 28.85%
Past 5 years rr_AverageAnnualReturnYear05 8.82%
Past 10 years rr_AverageAnnualReturnYear10 11.67%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Return Before Taxes | Fidelity Mega Cap Stock Fund- Class I  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Class I - Return Before Taxes</b></font>
Past 1 year rr_AverageAnnualReturnYear01 31.12%
Past 5 years rr_AverageAnnualReturnYear05 9.93%
Past 10 years rr_AverageAnnualReturnYear10 12.80%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Return Before Taxes | Fidelity Mega Cap Stock Fund-Class Z  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Class Z - Return Before Taxes</b></font>
Past 1 year rr_AverageAnnualReturnYear01 31.31%
Past 5 years rr_AverageAnnualReturnYear05 10.09%
Since Inception rr_AverageAnnualReturnSinceInception 11.32% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 13, 2013
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | After Taxes on Distributions | Fidelity Mega Cap Stock Fund-Class A  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Return After Taxes on Distributions</b></font>
Past 1 year rr_AverageAnnualReturnYear01 19.57%
Past 5 years rr_AverageAnnualReturnYear05 5.74%
Past 10 years rr_AverageAnnualReturnYear10 10.26%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | After Taxes on Distributions and Sales | Fidelity Mega Cap Stock Fund-Class A  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Mega Cap Stock Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Return After Taxes on Distributions and Sale of Fund Shares</b></font>
Past 1 year rr_AverageAnnualReturnYear01 16.02%
Past 5 years rr_AverageAnnualReturnYear05 6.21%
Past 10 years rr_AverageAnnualReturnYear10 9.59%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | S&P 500® Index(reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Past 1 year rr_AverageAnnualReturnYear01 31.49%
Past 5 years rr_AverageAnnualReturnYear05 11.70%
Past 10 years rr_AverageAnnualReturnYear10 13.56%
06.30 Fidelity Mega Cap Stock Fund AMCIZ PRO-11 | Fidelity Mega Cap Stock Fund | Russell Top 200® Index(reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Past 1 year rr_AverageAnnualReturnYear01 31.75%
Past 5 years rr_AverageAnnualReturnYear05 12.34%
Past 10 years rr_AverageAnnualReturnYear10 13.67%
[1] Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.
[2] On Class C shares redeemed less than one year after purchase.
[3] Since inception August 13, 2013.