v3.26.1
Investment Risks
Jun. 29, 2026
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | ValueInvestingMember  
Prospectus Line Items  
Risk [Text Block] "Value" Investing. "Value" stocks can perform differently from the market as a whole and other types of stocks and can continue to be undervalued by the market for long periods of time.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapValueIndexFund-PRO | Fidelity Large Cap Value Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | HighPortfolioTurnoverMember  
Prospectus Line Items  
Risk [Text Block] High Portfolio Turnover. High portfolio turnover (more than 100%) may result in increased transaction costs and potentially higher capital gains or losses. The effects of higher than normal portfolio turnover may adversely affect the fund's performance.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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. The fund will be concentrated to approximately the same extent that the fund's index concentrates in the securities of issuers in a particular industry .
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | MidCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | RulesBasedStrategyRiskMember  
Prospectus Line Items  
Risk [Text Block] Rules-Based Strategy Risk. Although the index uses a rules-based proprietary index methodology, there is no guarantee that this methodology will be successful. 
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Mid Cap Focused Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | HighPortfolioTurnoverMember  
Prospectus Line Items  
Risk [Text Block] High Portfolio Turnover. High portfolio turnover (more than 100%) may result in increased transaction costs and potentially higher capital gains or losses. The effects of higher than normal portfolio turnover may adversely affect the fund's performance.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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. The fund will be concentrated to approximately the same extent that the fund's index concentrates in the securities of issuers in a particular industry .
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | SmallCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | RulesBasedStrategyRiskMember  
Prospectus Line Items  
Risk [Text Block] Rules-Based Strategy Risk. Although the index uses a rules-based proprietary index methodology, there is no guarantee that this methodology will be successful. 
FidelityFlexMidCapFocusedandFlexSmallCapFocusedIndexFunds-ComboPRO | Fidelity Flex Small Cap Focused Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | MidCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Mid Cap Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | SmallCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityMidCapIndexSmallCapIndexFunds-ComboPRO | Fidelity Small Cap Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | Risk Nondiversified Status [Member]  
Prospectus Line Items  
Risk [Text Block] In addition, the fund may operate as a non-diversified fund under the 1940 Act to the approximate extent the index is non-diversified. A non-diversified fund may invest a greater portion of its assets in securities of a smaller number of individual issuers than a diversified fund. As a result, changes in the market value of a single investment could cause greater fluctuations in share price than would occur in a more diversified fund.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | GrowthInvestingMember  
Prospectus Line Items  
Risk [Text Block] "Growth" Investing. "Growth" stocks can perform differently from the market as a whole and other types of stocks and can be more volatile than other types of stocks.      
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityLargeCapGrowthIndexFund-PRO | Fidelity Large Cap Growth Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | MidCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | RulesBasedStrategyRiskMember  
Prospectus Line Items  
Risk [Text Block] Rules-Based Strategy Risk. Although the index uses a rules-based proprietary index methodology, there is no guarantee that this methodology will be successful. 
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Mid Cap Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | SecuritiesLendingRiskMember  
Prospectus Line Items  
Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | IssuerSpecificChangesMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | StockMarketVolatilityMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | PassiveManagementRiskMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | SmallCapInvestingMember  
Prospectus Line Items  
Risk [Text Block] 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.
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | RulesBasedStrategyRiskMember  
Prospectus Line Items  
Risk [Text Block] Rules-Based Strategy Risk. Although the index uses a rules-based proprietary index methodology, there is no guarantee that this methodology will be successful. 
FidelityFlexMidCapIndexFundFidelityFlexSmallCapIndexFund-ComboPRO | Fidelity Flex Small Cap Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | Risk Nondiversified Status [Member]  
Prospectus Line Items  
Risk [Text Block] In addition, the fund may operate as a non-diversified fund under the 1940 Act to the approximate extent the index is non-diversified. A non-diversified fund may invest a greater portion of its assets in securities of a smaller number of individual issuers than a diversified fund. As a result, changes in the market value of a single investment could cause greater fluctuations in share price than would occur in a more diversified fund.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | Risk Not Insured Depository Institution [Member]  
Prospectus Line Items  
Risk [Text Block] 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 .
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | GrowthInvestingMember  
Prospectus Line Items  
Risk [Text Block] "Growth" Investing. "Growth" stocks can perform differently from the market as a whole and other types of stocks and can be more volatile than other types of stocks.      
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | SecuritiesLendingRiskMember  
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Risk [Text Block] Securities Lending Risk. Securities lending involves the risk that the borrower may fail to return the securities loaned in a timely manner or at all. If the borrower defaults on its obligation to return the securities loaned because of insolvency or other reasons, a fund could experience delays and costs in recovering the securities loaned or in gaining access to the collateral.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | IssuerSpecificChangesMember  
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Risk [Text Block] 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.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | StockMarketVolatilityMember  
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Risk [Text Block] 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.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | PassiveManagementRiskMember  
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Risk [Text Block] 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. The fund will be concentrated to approximately the same extent that the fund's index concentrates in the securities of issuers in a particular industry.
FidelitySeriesLargeCapGrowthIndexFund-PRO | Fidelity Series Large Cap Growth Index Fund | CorrelationToIndexMember  
Prospectus Line Items  
Risk [Text Block] Correlation to Index. The performance of the fund and its underlying 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 the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.
Document Type 485BPOS