485BPOS

Securities Act of 1933 Registration No. 033-15983

Investment Company Act of 1940 Registration No. 811-05251

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 x

o Pre-Effective Amendment No.  ______

x Post-Effective Amendment No.  100

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940 x

x Amendment No.  100

Fidelity Concord Street Trust

 (Exact Name of Registrant as Specified in Charter)

245 Summer Street, Boston, Massachusetts 02210

(Address of Principal Executive Offices)(Zip Code)

Registrant’s Telephone Number: 617-563-7000

Marc Bryant, Secretary

245 Summer Street

Boston, Massachusetts 02210

(Name and Address of Agent for Service)

It is proposed that this filing will become effective immediately upon filing pursuant to paragraph (b) of Rule 485.

EXHIBIT INDEX

Exhibit	Exhibit No.
XBRL Instance Document	EX-101.INS
XBRL Taxonomy Extension Schema Document	EX-101.SCH
XBRL Taxonomy Extension Calculation Linkbase Document	EX-101.CAL
XBRL Taxonomy Extension Definition Linkbase Document	EX-101.DEF
XBRL Taxonomy Extension Labels Linkbase Document	EX-101.LAB
XBRL Taxonomy Extension Presentation Linkbase Document	EX-101.PRE

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No. 100 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Boston, and Commonwealth of Massachusetts, on the 17th day of May 2018.

	Fidelity Concord Street Trust
	By	/s/Stacie M. Smith
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||		Stacie M. Smith, President

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

(Signature)		(Title)	(Date)
/s/Stacie M. Smith		President and Treasurer	May 17, 2018
Stacie M. Smith		(Principal Executive Officer)
/s/Howard J. Galligan III		Chief Financial Officer	May 17, 2018
Howard J. Galligan III		(Principal Financial Officer)
/s/Jonathan Chiel	*	Trustee	May 17, 2018
Jonathan Chiel
/s/James C. Curvey	*	Trustee	May 17, 2018
James C. Curvey
/s/Dennis J. Dirks	*	Trustee	May 17, 2018
Dennis J. Dirks
/s/Donald F. Donahue	*	Trustee	May 17, 2018
Donald F. Donahue
/s/Alan J. Lacy	*	Trustee	May 17, 2018
Alan J. Lacy
/s/Ned C. Lautenbach	*	Trustee	May 17, 2018
Ned C. Lautenbach
/s/Joseph Mauriello	*	Trustee	May 17, 2018
Joseph Mauriello
/s/Charles S. Morrison	*	Trustee	May 17, 2018
Charles S. Morrison
/s/Cornelia M. Small	*	Trustee	May 17, 2018
Cornelia M. Small
/s/Garnett A. Smith	*	Trustee	May 17, 2018
Garnett A. Smith
/s/David M. Thomas	*	Trustee	May 17, 2018
David M. Thomas

*	By:	/s/Megan C. Johnson
		Megan C. Johnson, pursuant to powers of attorney dated March 2, 2018 and October 5, 2016 and filed herewith.

POWER OF ATTORNEY

I, the undersigned Trustee of the following investment companies:

Fidelity Advisor Series VIII Fidelity Concord Street Trust Fidelity Investment Trust Fidelity Puritan Trust Fidelity Securities Fund Variable Insurance Products Fund

in addition to any other Fidelity Fund for which the undersigned individual serves as Director or Trustee (collectively, the “Funds”), hereby constitute and appoint Thomas C. Bogle, Marc R. Bryant, John V. O’Hanlon, Robert W. Helm, Megan C. Johnson, and Anthony H. Zacharski, each of them singly, my true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for me and in my name in the appropriate capacity, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in my name and behalf in connection therewith as said attorneys-in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  I hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof.  This power of attorney is effective for all documents filed on or after October 5, 2016.

WITNESS my hand on this 5^th day of October, 2016.

/s/Jonathan Chiel

Jonathan Chiel

POWER OF ATTORNEY

We, the undersigned Directors or Trustees, as the case may be, of the following investment companies:

Fidelity Advisor Series I Fidelity Advisor Series VII Fidelity Advisor Series VIII Fidelity Beacon Street Trust Fidelity Capital Trust Fidelity Central Investment Portfolios LLC Fidelity Commonwealth Trust Fidelity Commonwealth Trust II Fidelity Concord Street Trust Fidelity Congress Street Fund Fidelity Contrafund Fidelity Covington Trust Fidelity Destiny Portfolios Fidelity Devonshire Trust Fidelity Exchange Fund Fidelity Financial Trust Fidelity Hanover Street Trust Fidelity Hastings Street Trust Fidelity Investment Trust Fidelity Magellan Fund Fidelity Mt. Vernon Street Trust Fidelity Puritan Trust Fidelity Securities Fund Fidelity Select Portfolios Fidelity Summer Street Trust Fidelity Trend Fund Variable Insurance Products Fund Variable Insurance Products Fund II Variable Insurance Products Fund III Variable Insurance Products Fund IV

in addition to any other investment company for which Fidelity Management & Research Company (“FMR”) or an affiliate acts as investment adviser and for which the undersigned individuals serve as Directors or Trustees (collectively, the “Funds”), hereby revoke all previous powers of attorney we have given to sign and otherwise act in our names and behalf in matters involving any investment company for which FMR or an affiliate acts as investment adviser and hereby constitute and appoint Thomas C. Bogle, John V. O’Hanlon, Robert W. Helm, Megan C. Johnson, and Anthony H. Zacharski, each of them singly, our true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for us and in our names in the appropriate capacities, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in our names and behalf in connection therewith as said attorneys–in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  We hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof.  This power of attorney is effective for all documents filed on or after March 2, 2018.

WITNESS our hands on this second day of March 2018.

/s/ James C. Curvey	/s/ Joseph Mauriello
James C. Curvey	Joseph Mauriello
/s/ Dennis J. Dirks	/s/ Charles S. Morrison
Dennis J. Dirks	Charles S. Morrison
/s/ Donald F. Donahue	/s/ Cornelia M. Small
Donald F. Donahue	Cornelia M. Small
/s/ Alan J. Lacy	/s/ Garnett A. Smith
Alan J. Lacy	Garnett A. Smith
/s/ Ned C. Lautenbach	/s/ David M. Thomas
Ned C. Lautenbach	David M. Thomas

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Feb. 28, 2018
Registrant Name	dei_EntityRegistrantName	FIDELITY CONCORD STREET TRUST
Central Index Key	dei_EntityCentralIndexKey	0000819118
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Apr. 27, 2018
Document Effective Date	dei_DocumentEffectiveDate	Apr. 28, 2018
Prospectus Date	rr_ProspectusDate	Apr. 28, 2018

XML

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund

Fund Summary

Fund/Class:
Fidelity® 500 Index Fund/Institutional, Institutional Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® 500 Index Fund}	02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 Fidelity® 500 Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 - Fidelity® 500 Index Fund	Fidelity 500 Index Fund-Institutional Class		Fidelity 500 Index Fund-Institutional Premium Class
Management fee	0.015%		0.015%
Distribution and/or Service (12b-1) fees	none		none
Other expenses	0.015%	[1]	none
Total annual operating expenses	0.03%		0.015%

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:

Sell All Shares

Expense Example {- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 - Fidelity® 500 Index Fund - USD ($)	Fidelity 500 Index Fund-Institutional Class	Fidelity 500 Index Fund-Institutional Premium Class
1 year	$ 3	$ 2
3 years	10	5
5 years	17	8
10 years	$ 39	$ 19

Portfolio Turnover

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 4% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	12.56%	March 31, 2012
Lowest Quarter Return	-6.45%	September 30, 2015
Year-to-Date Return	-0.77%	March 31, 2018

Average Annual Returns

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 Institutional Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 - Fidelity® 500 Index Fund	Past 1 year	Past 5 years	Since Inception	[1]	Inception Date
Fidelity 500 Index Fund-Institutional Class					May 04, 2011
Fidelity 500 Index Fund-Institutional Class | Return Before Taxes	21.79%	15.76%	13.19%
Fidelity 500 Index Fund-Institutional Class | After Taxes on Distributions	21.17%	15.11%	12.61%		May 04, 2011
Fidelity 500 Index Fund-Institutional Class | After Taxes on Distributions and Sales	12.75%	12.59%	10.64%		May 04, 2011
Fidelity 500 Index Fund-Institutional Premium Class					May 04, 2011
Fidelity 500 Index Fund-Institutional Premium Class | Return Before Taxes	21.81%	15.78%	13.21%
S&P 500® Index(reflects no deduction for fees, expenses, or taxes)	21.83%	15.79%	13.22%

[1] Adjusted to reflect current fees.

[1] From May 4, 2011

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® 500 Index Fund/Institutional, Institutional Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 4% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

4.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	12.56%	March 31, 2012
Lowest Quarter Return	-6.45%	September 30, 2015
Year-to-Date Return	-0.77%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Institutional Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Institutional Class 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).

For the periods ended December 31, 2017

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | Fidelity 500 Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.015%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.03%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

1 year

rr_ExpenseExampleYear01

$ 3

3 years

rr_ExpenseExampleYear03

10

5 years

rr_ExpenseExampleYear05

17

10 years

rr_ExpenseExampleYear10

$ 39

2012

rr_AnnualReturn2012

15.96%

2013

rr_AnnualReturn2013

32.35%

2014

rr_AnnualReturn2014

13.65%

2015

rr_AnnualReturn2015

1.36%

2016

rr_AnnualReturn2016

11.93%

2017

rr_AnnualReturn2017

21.79%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.77%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

12.56%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2015

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(6.45%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 04, 2011

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | Fidelity 500 Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual operating expenses

rr_ExpensesOverAssets

0.015%

1 year

rr_ExpenseExampleYear01

$ 2

3 years

rr_ExpenseExampleYear03

5

5 years

rr_ExpenseExampleYear05

8

10 years

rr_ExpenseExampleYear10

$ 19

Inception Date

rr_AverageAnnualReturnInceptionDate

May 04, 2011

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | Return Before Taxes | Fidelity 500 Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.79%

Past 5 years

rr_AverageAnnualReturnYear05

15.76%

Since Inception

rr_AverageAnnualReturnSinceInception

13.19%

^[2]

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | Return Before Taxes | Fidelity 500 Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.81%

Past 5 years

rr_AverageAnnualReturnYear05

15.78%

Since Inception

rr_AverageAnnualReturnSinceInception

13.21%

^[2]

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | After Taxes on Distributions | Fidelity 500 Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

21.17%

Past 5 years

rr_AverageAnnualReturnYear05

15.11%

Since Inception

rr_AverageAnnualReturnSinceInception

12.61%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

May 04, 2011

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | After Taxes on Distributions and Sales | Fidelity 500 Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

12.75%

Past 5 years

rr_AverageAnnualReturnYear05

12.59%

Since Inception

rr_AverageAnnualReturnSinceInception

10.64%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

May 04, 2011

02.28 Fidelity 500 Index Fund Institutional, Institutional Premium PRO-08 | Fidelity® 500 Index Fund | S&P 500® Index(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

21.83%

Past 5 years

rr_AverageAnnualReturnYear05

15.79%

Since Inception

rr_AverageAnnualReturnSinceInception

13.22%

^[2]

[1] Adjusted to reflect current fees.

[2] From May 4, 2011

XML

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund

Fund Summary

Fund/Class:
Fidelity® 500 Index Fund/Investor, Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® 500 Index Fund}	02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 Fidelity® 500 Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 - Fidelity® 500 Index Fund	Fidelity 500 Index Fund-Investor Class	Fidelity 500 Index Fund-Premium Class
Management fee	0.015%	0.015%
Distribution and/or Service (12b-1) fees	none	none
Other expenses	0.075%	0.02%	[1]
Total annual operating expenses	0.09%	0.035%

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:

Sell All Shares

Expense Example {- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 - Fidelity® 500 Index Fund - USD ($)	Fidelity 500 Index Fund-Investor Class	Fidelity 500 Index Fund-Premium Class
1 year	$ 9	$ 4
3 years	29	11
5 years	51	20
10 years	$ 115	$ 45

Portfolio Turnover

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 4% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Investor Class:	Returns	Quarter ended
Highest Quarter Return	15.95%	June 30, 2009
Lowest Quarter Return	-21.95%	December 31, 2008
Year-to-Date Return	-0.78%	March 31, 2018

Average Annual Returns

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 Investor Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® 500 Index Fund} - 02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 - Fidelity® 500 Index Fund	Past 1 year	Past 5 years	Past 10 years
Fidelity 500 Index Fund-Investor Class | Return Before Taxes	21.72%	15.69%	8.42%
Fidelity 500 Index Fund-Investor Class | After Taxes on Distributions	21.13%	15.07%	7.96%
Fidelity 500 Index Fund-Investor Class | After Taxes on Distributions and Sales	12.71%	12.55%	6.78%
Fidelity 500 Index Fund-Premium Class | Return Before Taxes	21.79%	15.74%	8.47%
S&P 500® Index(reflects no deduction for fees, expenses, or taxes)	21.83%	15.79%	8.50%

[1] Adjusted to reflect current fees.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® 500 Index Fund/Investor, Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 4% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

4.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Investor Class:	Returns	Quarter ended
Highest Quarter Return	15.95%	June 30, 2009
Lowest Quarter Return	-21.95%	December 31, 2008
Year-to-Date Return	-0.78%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Investor Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Investor Class 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).

For the periods ended December 31, 2017

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | Fidelity 500 Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.075%

Total annual operating expenses

rr_ExpensesOverAssets

0.09%

1 year

rr_ExpenseExampleYear01

$ 9

3 years

rr_ExpenseExampleYear03

29

5 years

rr_ExpenseExampleYear05

51

10 years

rr_ExpenseExampleYear10

$ 115

2008

rr_AnnualReturn2008

(37.03%)

2009

rr_AnnualReturn2009

26.51%

2010

rr_AnnualReturn2010

14.98%

2011

rr_AnnualReturn2011

2.03%

2012

rr_AnnualReturn2012

15.93%

2013

rr_AnnualReturn2013

32.25%

2014

rr_AnnualReturn2014

13.59%

2015

rr_AnnualReturn2015

1.31%

2016

rr_AnnualReturn2016

11.87%

2017

rr_AnnualReturn2017

21.72%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.78%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.95%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.95%)

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | Fidelity 500 Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.02%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.035%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

1 year

rr_ExpenseExampleYear01

$ 4

3 years

rr_ExpenseExampleYear03

11

5 years

rr_ExpenseExampleYear05

20

10 years

rr_ExpenseExampleYear10

$ 45

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | Return Before Taxes | Fidelity 500 Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Investor Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.72%

Past 5 years

rr_AverageAnnualReturnYear05

15.69%

Past 10 years

rr_AverageAnnualReturnYear10

8.42%

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | Return Before Taxes | Fidelity 500 Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.79%

Past 5 years

rr_AverageAnnualReturnYear05

15.74%

Past 10 years

rr_AverageAnnualReturnYear10

8.47%

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | After Taxes on Distributions | Fidelity 500 Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

21.13%

Past 5 years

rr_AverageAnnualReturnYear05

15.07%

Past 10 years

rr_AverageAnnualReturnYear10

7.96%

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | After Taxes on Distributions and Sales | Fidelity 500 Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® 500 Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

12.71%

Past 5 years

rr_AverageAnnualReturnYear05

12.55%

Past 10 years

rr_AverageAnnualReturnYear10

6.78%

02.28 Fidelity 500 Index Fund Investor, Premium PRO-07 | Fidelity® 500 Index Fund | S&P 500® Index(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

21.83%

Past 5 years

rr_AverageAnnualReturnYear05

15.79%

Past 10 years

rr_AverageAnnualReturnYear10

8.50%

[1] Adjusted to reflect current fees.

XML

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund

Fund Summary

Fund/Class:
Fidelity® Extended Market Index Fund/Institutional Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of stocks of mid- to small-capitalization United States companies.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® Extended Market Index Fund}	02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 Fidelity® Extended Market Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® Extended Market Index Fund}	02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 Fidelity® Extended Market Index Fund Fidelity Extended Market Index Fund-Institutional Premium Class
Management fee	0.045%
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual operating expenses	0.045%

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:

Sell All Shares

Expense Example {- Fidelity® Extended Market Index Fund}	02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 Fidelity® Extended Market Index Fund Fidelity Extended Market Index Fund-Institutional Premium Class USD ($)
1 year	$ 5
3 years	15
5 years	25
10 years	$ 58

Portfolio Turnover

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 11% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Completion Total Stock Market Index℠, which represents the performance of stocks of mid- to small-capitalization U.S. companies.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Completion Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Mid Cap Investing. The value of securities of medium size, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

• Small Cap Investing. The value of securities of smaller, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	14.38%	March 31, 2012
Lowest Quarter Return	-10.55%	September 30, 2015
Year-to-Date Return	0.15%	March 31, 2018

Average Annual Returns

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® Extended Market Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® Extended Market Index Fund	Past 1 year	Past 5 years	Since Inception	[1]	Inception Date
Fidelity Extended Market Index Fund-Institutional Premium Class					Sep. 08, 2011
Fidelity Extended Market Index Fund-Institutional Premium Class | Return Before Taxes	18.22%	14.60%	15.17%
Fidelity Extended Market Index Fund-Institutional Premium Class | After Taxes on Distributions	16.55%	13.17%	13.81%		Sep. 08, 2011
Fidelity Extended Market Index Fund-Institutional Premium Class | After Taxes on Distributions and Sales	11.41%	11.39%	12.08%		Sep. 08, 2011
Dow Jones U.S. Completion Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)	18.12%	14.43%	15.00%

[1] From September 8, 2011

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® Extended Market Index Fund/Institutional Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of stocks of mid- to small-capitalization United States companies.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 11% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

11.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Completion Total Stock Market Index℠, which represents the performance of stocks of mid- to small-capitalization U.S. companies.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Completion Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Mid Cap Investing. The value of securities of medium size, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

• Small Cap Investing. The value of securities of smaller, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

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.fidelity.com for more recent performance 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.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	14.38%	March 31, 2012
Lowest Quarter Return	-10.55%	September 30, 2015
Year-to-Date Return	0.15%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

For the periods ended December 31, 2017

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund | Fidelity Extended Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual operating expenses

rr_ExpensesOverAssets

0.045%

1 year

rr_ExpenseExampleYear01

$ 5

3 years

rr_ExpenseExampleYear03

15

5 years

rr_ExpenseExampleYear05

25

10 years

rr_ExpenseExampleYear10

$ 58

2012

rr_AnnualReturn2012

18.05%

2013

rr_AnnualReturn2013

38.25%

2014

rr_AnnualReturn2014

7.71%

2015

rr_AnnualReturn2015

(3.29%)

2016

rr_AnnualReturn2016

16.11%

2017

rr_AnnualReturn2017

18.22%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.15%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.38%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2015

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(10.55%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund | Return Before Taxes | Fidelity Extended Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

18.22%

Past 5 years

rr_AverageAnnualReturnYear05

14.60%

Since Inception

rr_AverageAnnualReturnSinceInception

15.17%

^[1]

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund | After Taxes on Distributions | Fidelity Extended Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

16.55%

Past 5 years

rr_AverageAnnualReturnYear05

13.17%

Since Inception

rr_AverageAnnualReturnSinceInception

13.81%

^[1]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund | After Taxes on Distributions and Sales | Fidelity Extended Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

11.41%

Past 5 years

rr_AverageAnnualReturnYear05

11.39%

Since Inception

rr_AverageAnnualReturnSinceInception

12.08%

^[1]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Extended Market Index Fund | Dow Jones U.S. Completion Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

18.12%

Past 5 years

rr_AverageAnnualReturnYear05

14.43%

Since Inception

rr_AverageAnnualReturnSinceInception

15.00%

^[1]

[1] From September 8, 2011

XML

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund

Fund Summary

Fund/Class:
Fidelity® International Index Fund/Institutional, Institutional Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of foreign stock markets.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® International Index Fund}	02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 Fidelity® International Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® International Index Fund		Fidelity International Index Fund-Institutional Class	Fidelity International Index Fund-Institutional Premium Class
Management fee	[1]	0.045%	0.045%
Distribution and/or Service (12b-1) fees		none	none
Other expenses	[1]	0.005%	none
Total annual operating expenses		0.05%	0.045%

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:

Sell All Shares

Expense Example {- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® International Index Fund - USD ($)	Fidelity International Index Fund-Institutional Class	Fidelity International Index Fund-Institutional Premium Class
1 year	$ 5	$ 5
3 years	16	15
5 years	28	25
10 years	$ 64	$ 58

Portfolio Turnover

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 2% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the MSCI EAFE Index, which represents the performance of foreign stock markets.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, earnings growth, and country weightings to attempt to replicate the returns of the MSCI EAFE Index.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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. Foreign exchange rates also can be extremely volatile.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	11.39%	September 30, 2013
Lowest Quarter Return	-10.06%	September 30, 2015
Year-to-Date Return	-0.93%	March 31, 2018

Average Annual Returns

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 Institutional Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® International Index Fund	Past 1 year	Past 5 years	Since Inception	[1]	Inception Date
Fidelity International Index Fund-Institutional Class					Sep. 08, 2011
Fidelity International Index Fund-Institutional Class | Return Before Taxes	25.33%	7.79%	8.78%
Fidelity International Index Fund-Institutional Class | After Taxes on Distributions	24.69%	7.14%	8.15%		Sep. 08, 2011
Fidelity International Index Fund-Institutional Class | After Taxes on Distributions and Sales	15.02%	6.11%	7.06%		Sep. 08, 2011
Fidelity International Index Fund-Institutional Premium Class					Sep. 08, 2011
Fidelity International Index Fund-Institutional Premium Class | Return Before Taxes	25.38%	7.80%	8.79%
MSCI EAFE Index(reflects no deduction for fees, expenses, or taxes)	25.29%	8.07%	8.72%

[1] Adjusted to reflect current fees.

[1] From September 8, 2011

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® International Index Fund/Institutional, Institutional Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of foreign stock markets.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 2% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

2.00%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the MSCI EAFE Index, which represents the performance of foreign stock markets.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, earnings growth, and country weightings to attempt to replicate the returns of the MSCI EAFE Index.

• Lending securities to earn income for the fund.

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. Foreign exchange rates also can be extremely volatile.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	11.39%	September 30, 2013
Lowest Quarter Return	-10.06%	September 30, 2015
Year-to-Date Return	-0.93%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Institutional Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Institutional Class 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).

For the periods ended December 31, 2017

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | Fidelity International Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

^[1]

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.005%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.05%

1 year

rr_ExpenseExampleYear01

$ 5

3 years

rr_ExpenseExampleYear03

16

5 years

rr_ExpenseExampleYear05

28

10 years

rr_ExpenseExampleYear10

$ 64

2012

rr_AnnualReturn2012

18.84%

2013

rr_AnnualReturn2013

21.86%

2014

rr_AnnualReturn2014

(5.32%)

2015

rr_AnnualReturn2015

(0.74%)

2016

rr_AnnualReturn2016

1.36%

2017

rr_AnnualReturn2017

25.33%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.93%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2013

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

11.39%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2015

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(10.06%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | Fidelity International Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

^[1]

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.045%

1 year

rr_ExpenseExampleYear01

$ 5

3 years

rr_ExpenseExampleYear03

15

5 years

rr_ExpenseExampleYear05

25

10 years

rr_ExpenseExampleYear10

$ 58

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | Return Before Taxes | Fidelity International Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

25.33%

Past 5 years

rr_AverageAnnualReturnYear05

7.79%

Since Inception

rr_AverageAnnualReturnSinceInception

8.78%

^[2]

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | Return Before Taxes | Fidelity International Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

25.38%

Past 5 years

rr_AverageAnnualReturnYear05

7.80%

Since Inception

rr_AverageAnnualReturnSinceInception

8.79%

^[2]

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | After Taxes on Distributions | Fidelity International Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

24.69%

Past 5 years

rr_AverageAnnualReturnYear05

7.14%

Since Inception

rr_AverageAnnualReturnSinceInception

8.15%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | After Taxes on Distributions and Sales | Fidelity International Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

15.02%

Past 5 years

rr_AverageAnnualReturnYear05

6.11%

Since Inception

rr_AverageAnnualReturnSinceInception

7.06%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® International Index Fund | MSCI EAFE Index(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

25.29%

Past 5 years

rr_AverageAnnualReturnYear05

8.07%

Since Inception

rr_AverageAnnualReturnSinceInception

8.72%

^[2]

[1] Adjusted to reflect current fees.

[2] From September 8, 2011

XML

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/Institutional, Institutional Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® Total Market Index Fund}	02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 Fidelity® Total Market Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® Total Market Index Fund	Fidelity Total Market Index Fund-Institutional Class		Fidelity Total Market Index Fund-Institutional Premium Class
Management fee	0.015%		0.015%
Distribution and/or Service (12b-1) fees	none		none
Other expenses	0.015%	[1]	none
Total annual operating expenses	0.03%		0.015%

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:

Sell All Shares

Expense Example {- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® Total Market Index Fund - USD ($)	Fidelity Total Market Index Fund-Institutional Class	Fidelity Total Market Index Fund-Institutional Premium Class
1 year	$ 3	$ 2
3 years	10	5
5 years	17	8
10 years	$ 39	$ 19

Portfolio Turnover

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 2% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	12.90%	March 31, 2012
Lowest Quarter Return	-7.26%	September 30, 2015
Year-to-Date Return	-0.60%	March 31, 2018

Average Annual Returns

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 Institutional Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 - Fidelity® Total Market Index Fund	Past 1 year	Past 5 years	Since Inception	[1]	Inception Date
Fidelity Total Market Index Fund-Institutional Class					Sep. 08, 2011
Fidelity Total Market Index Fund-Institutional Class | Return Before Taxes	21.16%	15.53%	15.95%
Fidelity Total Market Index Fund-Institutional Class | After Taxes on Distributions	20.46%	14.94%	15.39%		Sep. 08, 2011
Fidelity Total Market Index Fund-Institutional Class | After Taxes on Distributions and Sales	12.48%	12.43%	13.00%		Sep. 08, 2011
Fidelity Total Market Index Fund-Institutional Premium Class					Sep. 08, 2011
Fidelity Total Market Index Fund-Institutional Premium Class | Return Before Taxes	21.18%	15.54%	15.96%
Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)	21.16%	15.52%	15.95%

[1] Adjusted to reflect current fees.

[1] From September 8, 2011

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/Institutional, Institutional Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 2% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

2.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Institutional Class:	Returns	Quarter ended
Highest Quarter Return	12.90%	March 31, 2012
Lowest Quarter Return	-7.26%	September 30, 2015
Year-to-Date Return	-0.60%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Institutional Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Institutional Class 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).

For the periods ended December 31, 2017

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | Fidelity Total Market Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.015%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.03%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

1 year

rr_ExpenseExampleYear01

$ 3

3 years

rr_ExpenseExampleYear03

10

5 years

rr_ExpenseExampleYear05

17

10 years

rr_ExpenseExampleYear10

$ 39

2012

rr_AnnualReturn2012

16.34%

2013

rr_AnnualReturn2013

33.42%

2014

rr_AnnualReturn2014

12.46%

2015

rr_AnnualReturn2015

0.47%

2016

rr_AnnualReturn2016

12.68%

2017

rr_AnnualReturn2017

21.16%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.60%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

12.90%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2015

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(7.26%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | Fidelity Total Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual operating expenses

rr_ExpensesOverAssets

0.015%

1 year

rr_ExpenseExampleYear01

$ 2

3 years

rr_ExpenseExampleYear03

5

5 years

rr_ExpenseExampleYear05

8

10 years

rr_ExpenseExampleYear10

$ 19

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | Return Before Taxes | Fidelity Total Market Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.16%

Past 5 years

rr_AverageAnnualReturnYear05

15.53%

Since Inception

rr_AverageAnnualReturnSinceInception

15.95%

^[2]

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | Return Before Taxes | Fidelity Total Market Index Fund-Institutional Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Institutional Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.18%

Past 5 years

rr_AverageAnnualReturnYear05

15.54%

Since Inception

rr_AverageAnnualReturnSinceInception

15.96%

^[2]

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | After Taxes on Distributions | Fidelity Total Market Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

20.46%

Past 5 years

rr_AverageAnnualReturnYear05

14.94%

Since Inception

rr_AverageAnnualReturnSinceInception

15.39%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | After Taxes on Distributions and Sales | Fidelity Total Market Index Fund-Institutional Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

12.48%

Past 5 years

rr_AverageAnnualReturnYear05

12.43%

Since Inception

rr_AverageAnnualReturnSinceInception

13.00%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 08, 2011

02.28 Fidelity Index Funds Institutional, Institutional Premium Combo PRO-07 | Fidelity® Total Market Index Fund | Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

21.16%

Past 5 years

rr_AverageAnnualReturnYear05

15.52%

Since Inception

rr_AverageAnnualReturnSinceInception

15.95%

^[2]

[1] Adjusted to reflect current fees.

[2] From September 8, 2011

XML

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund

Fund Summary

Fund/Class:
Fidelity® Extended Market Index Fund/Investor, Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of stocks of mid- to small-capitalization United States companies.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® Extended Market Index Fund}	02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 Fidelity® Extended Market Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® Extended Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Extended Market Index Fund	Fidelity Extended Market Index Fund-Investor Class	Fidelity Extended Market Index Fund-Premium Class
Management fee	0.045%	0.045%
Distribution and/or Service (12b-1) fees	none	none
Other expenses	0.055%	0.025%
Total annual operating expenses	0.10%	0.07%

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:

Sell All Shares

Expense Example {- Fidelity® Extended Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Extended Market Index Fund - USD ($)	Fidelity Extended Market Index Fund-Investor Class	Fidelity Extended Market Index Fund-Premium Class
1 year	$ 10	$ 7
3 years	32	23
5 years	56	40
10 years	$ 128	$ 90

Portfolio Turnover

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 11% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Completion Total Stock Market Index℠, which represents the performance of stocks of mid- to small-capitalization U.S. companies.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Completion Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Mid Cap Investing. The value of securities of medium size, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

• Small Cap Investing. The value of securities of smaller, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Investor Class:	Returns	Quarter ended
Highest Quarter Return	20.64%	June 30, 2009
Lowest Quarter Return	-26.35%	December 31, 2008
Year-to-Date Return	0.15%	March 31, 2018

Average Annual Returns

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 Investor Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® Extended Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Extended Market Index Fund	Past 1 year	Past 5 years	Past 10 years
Fidelity Extended Market Index Fund-Investor Class | Return Before Taxes	18.15%	14.55%	9.24%
Fidelity Extended Market Index Fund-Investor Class | After Taxes on Distributions	16.51%	13.14%	8.23%
Fidelity Extended Market Index Fund-Investor Class | After Taxes on Distributions and Sales	11.37%	11.36%	7.30%
Fidelity Extended Market Index Fund-Premium Class | Return Before Taxes	18.18%	14.58%	9.28%
Dow Jones U.S. Completion Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)	18.12%	14.43%	9.15%

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® Extended Market Index Fund/Investor, Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of stocks of mid- to small-capitalization United States companies.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 11% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

11.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Completion Total Stock Market Index℠, which represents the performance of stocks of mid- to small-capitalization U.S. companies.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Completion Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Mid Cap Investing. The value of securities of medium size, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

• Small Cap Investing. The value of securities of smaller, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

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.fidelity.com for more recent performance 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.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 for Investor Class:	Returns	Quarter ended
Highest Quarter Return	20.64%	June 30, 2009
Lowest Quarter Return	-26.35%	December 31, 2008
Year-to-Date Return	0.15%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Investor Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Investor Class 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).

For the periods ended December 31, 2017

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | Fidelity Extended Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.055%

Total annual operating expenses

rr_ExpensesOverAssets

0.10%

1 year

rr_ExpenseExampleYear01

$ 10

3 years

rr_ExpenseExampleYear03

32

5 years

rr_ExpenseExampleYear05

56

10 years

rr_ExpenseExampleYear10

$ 128

2008

rr_AnnualReturn2008

(38.45%)

2009

rr_AnnualReturn2009

36.65%

2010

rr_AnnualReturn2010

28.58%

2011

rr_AnnualReturn2011

(3.82%)

2012

rr_AnnualReturn2012

18.01%

2013

rr_AnnualReturn2013

38.19%

2014

rr_AnnualReturn2014

7.68%

2015

rr_AnnualReturn2015

(3.35%)

2016

rr_AnnualReturn2016

16.07%

2017

rr_AnnualReturn2017

18.15%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.15%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

20.64%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(26.35%)

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | Fidelity Extended Market Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.025%

Total annual operating expenses

rr_ExpensesOverAssets

0.07%

1 year

rr_ExpenseExampleYear01

$ 7

3 years

rr_ExpenseExampleYear03

23

5 years

rr_ExpenseExampleYear05

40

10 years

rr_ExpenseExampleYear10

$ 90

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | Return Before Taxes | Fidelity Extended Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Investor Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

18.15%

Past 5 years

rr_AverageAnnualReturnYear05

14.55%

Past 10 years

rr_AverageAnnualReturnYear10

9.24%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | Return Before Taxes | Fidelity Extended Market Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

18.18%

Past 5 years

rr_AverageAnnualReturnYear05

14.58%

Past 10 years

rr_AverageAnnualReturnYear10

9.28%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | After Taxes on Distributions | Fidelity Extended Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

16.51%

Past 5 years

rr_AverageAnnualReturnYear05

13.14%

Past 10 years

rr_AverageAnnualReturnYear10

8.23%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | After Taxes on Distributions and Sales | Fidelity Extended Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Extended Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

11.37%

Past 5 years

rr_AverageAnnualReturnYear05

11.36%

Past 10 years

rr_AverageAnnualReturnYear10

7.30%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Extended Market Index Fund | Dow Jones U.S. Completion Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

18.12%

Past 5 years

rr_AverageAnnualReturnYear05

14.43%

Past 10 years

rr_AverageAnnualReturnYear10

9.15%

XML

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund

Fund Summary

Fund/Class:
Fidelity® International Index Fund/Investor, Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of foreign stock markets.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® International Index Fund}	02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 Fidelity® International Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® International Index Fund		Fidelity International Index Fund-Investor Class	Fidelity International Index Fund-Premium Class
Management fee	[1]	0.045%	0.045%
Distribution and/or Service (12b-1) fees		none	none
Other expenses	[1]	0.115%	0.015%
Total annual operating expenses		0.16%	0.06%

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:

Sell All Shares

Expense Example {- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® International Index Fund - USD ($)	Fidelity International Index Fund-Investor Class	Fidelity International Index Fund-Premium Class
1 year	$ 16	$ 6
3 years	52	19
5 years	90	34
10 years	$ 205	$ 77

Portfolio Turnover

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 2% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the MSCI EAFE Index, which represents the performance of foreign stock markets.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, earnings growth, and country weightings to attempt to replicate the returns of the MSCI EAFE Index.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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. Foreign exchange rates also can be extremely volatile.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Investor Class:	Returns	Quarter ended
Highest Quarter Return	25.40%	June 30, 2009
Lowest Quarter Return	-19.75%	September 30, 2011
Year-to-Date Return	-0.97%	March 31, 2018

Average Annual Returns

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 Investor Class 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, 2017

Average Annual Total Returns{- Fidelity® International Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® International Index Fund	Past 1 year	Past 5 years	Past 10 years
Fidelity International Index Fund-Investor Class | Return Before Taxes	25.23%	7.65%	2.02%
Fidelity International Index Fund-Investor Class | After Taxes on Distributions	24.63%	7.05%	1.59%
Fidelity International Index Fund-Investor Class | After Taxes on Distributions and Sales	14.96%	6.02%	1.66%
Fidelity International Index Fund-Premium Class | Return Before Taxes	25.35%	7.74%	2.09%
MSCI EAFE Index(reflects no deduction for fees, expenses, or taxes)	25.29%	8.07%	2.10%

[1] Adjusted to reflect current fees.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® International Index Fund/Investor, Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of foreign stock markets.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 2% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

2.00%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the MSCI EAFE Index, which represents the performance of foreign stock markets.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, earnings growth, and country weightings to attempt to replicate the returns of the MSCI EAFE Index.

• Lending securities to earn income for the fund.

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. Foreign exchange rates also can be extremely volatile.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Investor Class:	Returns	Quarter ended
Highest Quarter Return	25.40%	June 30, 2009
Lowest Quarter Return	-19.75%	September 30, 2011
Year-to-Date Return	-0.97%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Investor Class are shown in the table below and after-tax returns for other classes will vary.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

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.

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. After-tax returns for Investor Class 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, 2017

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | Fidelity International Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

^[1]

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.115%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.16%

1 year

rr_ExpenseExampleYear01

$ 16

3 years

rr_ExpenseExampleYear03

52

5 years

rr_ExpenseExampleYear05

90

10 years

rr_ExpenseExampleYear10

$ 205

2008

rr_AnnualReturn2008

(41.43%)

2009

rr_AnnualReturn2009

28.48%

2010

rr_AnnualReturn2010

7.70%

2011

rr_AnnualReturn2011

(12.15%)

2012

rr_AnnualReturn2012

18.69%

2013

rr_AnnualReturn2013

21.70%

2014

rr_AnnualReturn2014

(5.45%)

2015

rr_AnnualReturn2015

(0.87%)

2016

rr_AnnualReturn2016

1.20%

2017

rr_AnnualReturn2017

25.23%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.97%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

25.40%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.75%)

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | Fidelity International Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.045%

^[1]

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.015%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.06%

1 year

rr_ExpenseExampleYear01

$ 6

3 years

rr_ExpenseExampleYear03

19

5 years

rr_ExpenseExampleYear05

34

10 years

rr_ExpenseExampleYear10

$ 77

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | Return Before Taxes | Fidelity International Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Investor Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

25.23%

Past 5 years

rr_AverageAnnualReturnYear05

7.65%

Past 10 years

rr_AverageAnnualReturnYear10

2.02%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | Return Before Taxes | Fidelity International Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

25.35%

Past 5 years

rr_AverageAnnualReturnYear05

7.74%

Past 10 years

rr_AverageAnnualReturnYear10

2.09%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | After Taxes on Distributions | Fidelity International Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

24.63%

Past 5 years

rr_AverageAnnualReturnYear05

7.05%

Past 10 years

rr_AverageAnnualReturnYear10

1.59%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | After Taxes on Distributions and Sales | Fidelity International Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® International Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

14.96%

Past 5 years

rr_AverageAnnualReturnYear05

6.02%

Past 10 years

rr_AverageAnnualReturnYear10

1.66%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® International Index Fund | MSCI EAFE Index(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

25.29%

Past 5 years

rr_AverageAnnualReturnYear05

8.07%

Past 10 years

rr_AverageAnnualReturnYear10

2.10%

[1] Adjusted to reflect current fees.

XML

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/Investor, Premium

Investment Objective

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® Total Market Index Fund}	02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 Fidelity® Total Market Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Total Market Index Fund	Fidelity Total Market Index Fund-Investor Class	Fidelity Total Market Index Fund-Premium Class
Management fee	0.015%	0.015%
Distribution and/or Service (12b-1) fees	none	none
Other expenses	0.075%	0.02%	[1]
Total annual operating expenses	0.09%	0.035%

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:

Sell All Shares

Expense Example {- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Total Market Index Fund - USD ($)	Fidelity Total Market Index Fund-Investor Class	Fidelity Total Market Index Fund-Premium Class
1 year	$ 9	$ 4
3 years	29	11
5 years	51	20
10 years	$ 115	$ 45

Portfolio Turnover

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 2% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.fidelity.com for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart for Investor Class:	Returns	Quarter ended
Highest Quarter Return	16.77%	June 30, 2009
Lowest Quarter Return	-22.87%	December 31, 2008
Year-to-Date Return	-0.62%	March 31, 2018

Average Annual Returns

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 Investor Class 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).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® Total Market Index Fund} - 02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 - Fidelity® Total Market Index Fund	Past 1 year	Past 5 years	Past 10 years
Fidelity Total Market Index Fund-Investor Class | Return Before Taxes	21.08%	15.46%	8.60%
Fidelity Total Market Index Fund-Investor Class | After Taxes on Distributions	20.42%	14.90%	8.17%
Fidelity Total Market Index Fund-Investor Class | After Taxes on Distributions and Sales	12.43%	12.39%	6.94%
Fidelity Total Market Index Fund-Premium Class | Return Before Taxes	21.15%	15.51%	8.64%
Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)	21.16%	15.52%	8.66%

[1] Adjusted to reflect current fees.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/Investor, Premium

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 2% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

2.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.fidelity.com for more recent performance 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.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 for Investor Class:	Returns	Quarter ended
Highest Quarter Return	16.77%	June 30, 2009
Lowest Quarter Return	-22.87%	December 31, 2008
Year-to-Date Return	-0.62%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Investor Class are shown in the table below and after-tax returns for other classes will vary.

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. After-tax returns for Investor Class 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).

For the periods ended December 31, 2017

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | Fidelity Total Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.075%

Total annual operating expenses

rr_ExpensesOverAssets

0.09%

1 year

rr_ExpenseExampleYear01

$ 9

3 years

rr_ExpenseExampleYear03

29

5 years

rr_ExpenseExampleYear05

51

10 years

rr_ExpenseExampleYear10

$ 115

2008

rr_AnnualReturn2008

(37.18%)

2009

rr_AnnualReturn2009

28.39%

2010

rr_AnnualReturn2010

17.41%

2011

rr_AnnualReturn2011

0.98%

2012

rr_AnnualReturn2012

16.29%

2013

rr_AnnualReturn2013

33.37%

2014

rr_AnnualReturn2014

12.40%

2015

rr_AnnualReturn2015

0.41%

2016

rr_AnnualReturn2016

12.61%

2017

rr_AnnualReturn2017

21.08%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.62%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

16.77%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(22.87%)

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | Fidelity Total Market Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.02%

^[1]

Total annual operating expenses

rr_ExpensesOverAssets

0.035%

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Adjusted to reflect current fees.

1 year

rr_ExpenseExampleYear01

$ 4

3 years

rr_ExpenseExampleYear03

11

5 years

rr_ExpenseExampleYear05

20

10 years

rr_ExpenseExampleYear10

$ 45

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | Return Before Taxes | Fidelity Total Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Investor Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.08%

Past 5 years

rr_AverageAnnualReturnYear05

15.46%

Past 10 years

rr_AverageAnnualReturnYear10

8.60%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | Return Before Taxes | Fidelity Total Market Index Fund-Premium Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Premium Class - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.15%

Past 5 years

rr_AverageAnnualReturnYear05

15.51%

Past 10 years

rr_AverageAnnualReturnYear10

8.64%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | After Taxes on Distributions | Fidelity Total Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

20.42%

Past 5 years

rr_AverageAnnualReturnYear05

14.90%

Past 10 years

rr_AverageAnnualReturnYear10

8.17%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | After Taxes on Distributions and Sales | Fidelity Total Market Index Fund-Investor Class

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

12.43%

Past 5 years

rr_AverageAnnualReturnYear05

12.39%

Past 10 years

rr_AverageAnnualReturnYear10

6.94%

02.28 Fidelity Index Funds Investor, Premium Combo PRO-06 | Fidelity® Total Market Index Fund | Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

21.16%

Past 5 years

rr_AverageAnnualReturnYear05

15.52%

Past 10 years

rr_AverageAnnualReturnYear10

8.66%

[1] Adjusted to reflect current fees.

XML

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/F

Investment Objective

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity® Total Market Index Fund}	02.28 Fidelity Total Market Index Fund F PRO-05 Fidelity® Total Market Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity® Total Market Index Fund}	02.28 Fidelity Total Market Index Fund F PRO-05 Fidelity® Total Market Index Fund Fidelity Total Market Index Fund-Class F
Management fee	0.015%
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual operating expenses	0.015%

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:

Sell All Shares

Expense Example {- Fidelity® Total Market Index Fund}	02.28 Fidelity Total Market Index Fund F PRO-05 Fidelity® Total Market Index Fund Fidelity Total Market Index Fund-Class F USD ($)
1 year	$ 2
3 years	5
5 years	8
10 years	$ 19

Portfolio Turnover

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 2% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

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.401k.com and log in for more recent performance information.

Year-by-Year Returns

Calendar Years

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	12.90%	March 31, 2012
Lowest Quarter Return	-15.23%	September 30, 2011
Year-to-Date Return	-0.60%	March 31, 2018

Average Annual Returns

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

For the periods ended December 31, 2017

Average Annual Total Returns{- Fidelity® Total Market Index Fund} - 02.28 Fidelity Total Market Index Fund F PRO-05 - Fidelity® Total Market Index Fund	Past 1 year	Past 5 years	Since Inception	[1]	Inception Date
Fidelity Total Market Index Fund-Class F					Sep. 24, 2009
Fidelity Total Market Index Fund-Class F | Return Before Taxes	21.17%	15.54%	14.32%
Fidelity Total Market Index Fund-Class F | After Taxes on Distributions	20.47%	14.94%	13.81%		Sep. 24, 2009
Fidelity Total Market Index Fund-Class F | After Taxes on Distributions and Sales	12.48%	12.43%	11.83%		Sep. 24, 2009
Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)	21.16%	15.52%	14.33%

[1] From September 24, 2009

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity® Total Market Index Fund/F

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return of a broad range of United States stocks.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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 2% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

2.00%

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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the Dow Jones U.S. Total Stock Market Index℠, which represents the performance of a broad range of U.S. stocks.

• Using statistical sampling techniques based on such factors as capitalization, industry exposures, dividend yield, price/earnings (P/E) ratio, price/book (P/B) ratio, and earnings growth to attempt to replicate the returns of the Dow Jones U.S. Total Stock Market Index℠ using a smaller number of securities.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.401k.com and log in for more recent performance 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.401k.com and log in

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	12.90%	March 31, 2012
Lowest Quarter Return	-15.23%	September 30, 2011
Year-to-Date Return	-0.60%	March 31, 2018

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

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, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).

For the periods ended December 31, 2017

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund | Fidelity Total Market Index Fund-Class F

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.015%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual operating expenses

rr_ExpensesOverAssets

0.015%

1 year

rr_ExpenseExampleYear01

$ 2

3 years

rr_ExpenseExampleYear03

5

5 years

rr_ExpenseExampleYear05

8

10 years

rr_ExpenseExampleYear10

$ 19

2010

rr_AnnualReturn2010

17.44%

2011

rr_AnnualReturn2011

1.01%

2012

rr_AnnualReturn2012

16.37%

2013

rr_AnnualReturn2013

33.42%

2014

rr_AnnualReturn2014

12.49%

2015

rr_AnnualReturn2015

0.47%

2016

rr_AnnualReturn2016

12.67%

2017

rr_AnnualReturn2017

21.17%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2018

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

(0.60%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

12.90%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(15.23%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 24, 2009

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund | Return Before Taxes | Fidelity Total Market Index Fund-Class F

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

21.17%

Past 5 years

rr_AverageAnnualReturnYear05

15.54%

Since Inception

rr_AverageAnnualReturnSinceInception

14.32%

^[1]

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund | After Taxes on Distributions | Fidelity Total Market Index Fund-Class F

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

20.47%

Past 5 years

rr_AverageAnnualReturnYear05

14.94%

Since Inception

rr_AverageAnnualReturnSinceInception

13.81%

^[1]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 24, 2009

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund | After Taxes on Distributions and Sales | Fidelity Total Market Index Fund-Class F

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Fidelity® Total Market Index Fund

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

12.48%

Past 5 years

rr_AverageAnnualReturnYear05

12.43%

Since Inception

rr_AverageAnnualReturnSinceInception

11.83%

^[1]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 24, 2009

02.28 Fidelity Total Market Index Fund F PRO-05 | Fidelity® Total Market Index Fund | Dow Jones U.S. Total Stock Market Index℠(reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Past 1 year

rr_AverageAnnualReturnYear01

21.16%

Past 5 years

rr_AverageAnnualReturnYear05

15.52%

Since Inception

rr_AverageAnnualReturnSinceInception

14.33%

^[1]

[1] From September 24, 2009

XML

02.28 Fidelity Flex 500 Index Fund PRO-03 | Fidelity Flex℠ 500 Index Fund

Fund Summary

Fund:
Fidelity Flex℠ 500 Index Fund

Investment Objective

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees

Shareholder Fees {- Fidelity Flex℠ 500 Index Fund}	02.28 Fidelity Flex 500 Index Fund PRO-03 Fidelity Flex℠ 500 Index Fund USD ($)
(fees paid directly from your investment)	none

Annual Operating Expenses

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

Annual Operating Expenses {- Fidelity Flex℠ 500 Index Fund}	02.28 Fidelity Flex 500 Index Fund PRO-03 Fidelity Flex℠ 500 Index Fund Fidelity Flex 500 Index Fund-Default
Management fee	none
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual operating expenses	none	[1]

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. This example does not include any fees paid at the fee-based account or plan level. 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:

Sell All Shares

Expense Example {- Fidelity Flex℠ 500 Index Fund}	02.28 Fidelity Flex 500 Index Fund PRO-03 Fidelity Flex℠ 500 Index Fund Fidelity Flex 500 Index Fund-Default USD ($)
1 year	none
3 years	none
5 years	none
10 years	none

Portfolio Turnover

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. For the period from March 9, 2017 to February 28, 2018, the fund's portfolio turnover rate was 10% (annualized) of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

Principal Investment Risks

• 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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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.

Performance

Performance history will be available for the fund after the fund has been in operation for one calendar year.

[1] The fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY CONCORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Apr. 28, 2018

02.28 Fidelity Flex 500 Index Fund PRO-03 | Fidelity Flex℠ 500 Index Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund:
Fidelity Flex℠ 500 Index Fund

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks to provide investment results that correspond to the total return (i.e., the combination of capital changes and income) performance of common stocks publicly traded in the United States.

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)

rr_ShareholderFeeOther

none

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual 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. For the period from March 9, 2017 to February 28, 2018, the fund's portfolio turnover rate was 10% (annualized) of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

10.00%

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. This example does not include any fees paid at the fee-based account or plan level. 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:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in common stocks included in the S&P 500^® Index, which broadly represents the performance of common stocks publicly traded in the United States.

• Lending securities to earn income for the fund.

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.

• 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. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty.

• Correlation to Index. The performance of the fund and its index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from its index.

• Passive Management Risk. The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund’s index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

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

Performance history will be available for the fund after the fund has been in operation for one calendar year.

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.

02.28 Fidelity Flex 500 Index Fund PRO-03 | Fidelity Flex℠ 500 Index Fund | Fidelity Flex 500 Index Fund-Default

Risk/Return:

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

none

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual operating expenses

rr_ExpensesOverAssets

none

^[1]

1 year

rr_ExpenseExampleYear01

none

3 years

rr_ExpenseExampleYear03

none

5 years

rr_ExpenseExampleYear05

none

10 years

rr_ExpenseExampleYear10

none

[1] The fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY CONCORD STREET TRUST
Prospectus Date	rr_ProspectusDate	Apr. 28, 2018
Document Creation Date	dei_DocumentCreationDate	Apr. 27, 2018