v3.26.1
Investment Risks
Apr. 29, 2026
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond 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 .
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond Index Fund | 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond 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. 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond 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 .
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond Index Fund | 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond 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. 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond 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.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Short-Term Treasury Bond 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.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond 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 .
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond Index Fund | 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.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond 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. 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.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond 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.
FidelitySeriesLong-TermTreasuryBondIndexFund-PRO | Fidelity Series Long-Term Treasury Bond 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.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond 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 .
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond Index Fund | 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.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond 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. 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.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond 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.
FidelitySAIUSTreasuryBondIndexFund-PRO | Fidelity SAI U.S. Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond 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 .
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond Index Fund | 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond 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. 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Intermediate Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond 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 .
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond Index Fund | 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond 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. 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Long-Term Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond 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 .
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond Index Fund | 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond 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. 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond 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.
FidelityIntermediateLong-TermandShort-TermTreasuryBondIndexFunds-ComboPRO | Fidelity Short-Term Treasury Bond 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.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond Index Fund | Risk Lose Money [Member]  
Prospectus Line Items  
Risk [Text Block]   You could lose money by investing in the fund.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond 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 .
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond Index Fund | InterestRateChangesMember  
Prospectus Line Items  
Risk [Text Block] Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond Index Fund | 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.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond 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. 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.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond 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.
FidelitySAILong-TermTreasuryBondIndexFund-PRO | Fidelity SAI Long-Term Treasury Bond 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