Risk/Return Summary - FidelitySeriesLong-TermTreasuryBondIndexFund-PRO - FidelitySeriesLong-TermTreasuryBondIndexFund-PRO - Fidelity Series Long-Term Treasury Bond Index Fund	Apr. 29, 2025
Risk Lose Money [Text]
Prospectus Line Items
Risk Text Block	You could lose money by investing in the fund.
Risk Not Insured Depository Institution [Text]
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 .
InterestRateChangesMember
Prospectus Line Items
Risk Text Block	Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
USTreasuryObligationsMember
Prospectus Line Items
Risk Text Block	U.S. Treasury Obligations. U.S. Treasury obligations are high-quality securities issued or guaranteed by the U.S. Treasury providing minimal risk of loss of principal if held to maturity. Fluctuations in interest rates may cause the market value of such securities to vary.
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. A decline in the credit quality of an issuer or a provider of credit support (such as guarantees) or a maturity-shortening structure (such as demand and put features) for a security can cause the price of a security to decrease.
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.
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.

Risk/Return Summary - FidelitySeriesLong-TermTreasuryBondIndexFund-PRO - FidelitySeriesLong-TermTreasuryBondIndexFund-PRO - Fidelity Series Long-Term Treasury Bond Index Fund

Apr. 29, 2025

You could lose money by investing in the fund.

Risk Not Insured Depository Institution [Text]

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 .

InterestRateChangesMember

Prospectus Line Items

Risk Text Block

Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.

USTreasuryObligationsMember

Prospectus Line Items

Risk Text Block

U.S. Treasury Obligations. U.S. Treasury obligations are high-quality securities issued or guaranteed by the U.S. Treasury providing minimal risk of loss of principal if held to maturity. Fluctuations in interest rates may cause the market value of such securities to vary.

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. A decline in the credit quality of an issuer or a provider of credit support (such as guarantees) or a maturity-shortening structure (such as demand and put features) for a security can cause the price of a security to decrease.

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.

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.