Risk/Return Detail Data - FidelitySAIMunicipalIncomeFund-PRO - USD ($)			12 Months Ended											24 Months Ended		36 Months Ended		60 Months Ended		84 Months Ended		96 Months Ended		120 Months Ended
		Feb. 28, 2026	Feb. 28, 2026	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2026		Feb. 28, 2026		Feb. 28, 2026		Feb. 28, 2026		Feb. 28, 2026		Feb. 28, 2026
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund | Fidelity SAI Inflation-Protected Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.05%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.01%
Expenses (as a percentage of Assets)		0.06%
Fee Waiver or Reimbursement	[1]	(0.01%)
Net Expenses (as a percentage of Assets)		0.05%
Expense Example, with Redemption, 1 Year		$ 5
Expense Example, with Redemption, 3 Years		18
Expense Example, with Redemption, 5 Years		33
Expense Example, with Redemption, 10 Years		$ 76
Annual Return, Inception Date		Aug. 16, 2024
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			6.76%											4.09%	[2]
Annual Return [Percent]				6.76%
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® SAI Inflation-Protected Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® SAI Inflation-Protected Bond Index Fund seeks to provide investment results that correspond to the total return of the inflation-protected sector of the United States Treasury market.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Fee Waiver or Reimbursement over Assets, Date of Termination		Apr. 30, 2027
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 34 % of the average value of its portfolio.
Portfolio Turnover, Rate		34.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in inflation-protected debt securities included in the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index. The Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index is a market value-weighted index that measures the performance of inflation-protected securities issued by the U.S. Treasury. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index using a smaller number of securities. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the performance of the fund's shares over the past year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the performance of the fund's shares over the past year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Mar. 31, 2025
Highest Quarterly Return		4.17%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Dec. 31, 2025
Lowest Quarterly Return		(0.09%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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 .
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund | After Taxes on Distributions | Fidelity SAI Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			4.99%											2.66%	[2]
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund | After Taxes on Distributions and Sales | Fidelity SAI Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			4.00%											2.52%	[2]
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund | LB124
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index
Average Annual Return, Percent			7.01%											4.33%
FidelitySAIInflation-ProtectedBondIndexFund-PRO | Fidelity SAI Inflation-Protected Bond Index Fund | LB001
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Aggregate Bond Index
Average Annual Return, Percent			7.30%											4.02%
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | Fidelity International Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.06%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.00%
Expenses (as a percentage of Assets)		0.06%
Expense Example, with Redemption, 1 Year		$ 6
Expense Example, with Redemption, 3 Years		19
Expense Example, with Redemption, 5 Years		34
Expense Example, with Redemption, 10 Years		$ 77
Annual Return, Inception Date		Oct. 10, 2019
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			2.66%															0.23%		0.68%	[3]
Annual Return [Percent]				2.66%	4.64%	7.48%	(10.84%)	(1.74%)	4.33%
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® International Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® International Bond Index Fund seeks to provide a high level of current income.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions, which are not reflected in the tables and examples below.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 64 % of the average value of its portfolio.
Portfolio Turnover, Rate		64.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in securities included in the Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD). The Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD) is a multi-currency benchmark that includes fixed-rate treasury, government-related, corporate and securitized bonds from developed markets issuers while excluding USD denominated debt. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD) using a smaller number of securities. Hedging the fund's foreign currency exposures utilizing forward foreign currency exchange contracts. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default), options, and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and additional indexes over various periods of time. The additional indexes have characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. Prior to September 26, 2025, the fund compared its performance to a different benchmark. The fund's historical performance may not represent its current investment policies. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and additional indexes over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Dec. 31, 2023
Highest Quarterly Return		5.38%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Mar. 31, 2022
Lowest Quarterly Return		(4.61%)
Performance Table Heading		Average Annual Returns
Performance Table Market Index Changed		Effective September 26, 2025, the fund began comparing its performance to the Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD) rather than the Bloomberg Global Aggregate ex-USD Float Adjusted RIC Diversified Index (Hedged USD) because Fidelity Management & Research Company LLC (FMR) (the Adviser) believes the Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD) mitigates country-specific risk and volatility and also reduces currency hedging costs.
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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.
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | After Taxes on Distributions | Fidelity International Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			1.00%															(0.74%)		(0.16%)	[3]
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | After Taxes on Distributions and Sales | Fidelity International Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			1.57%															(0.24%)		0.16%	[3]
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | IXRNK
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Fidelity International Bond Linked Index℠
Average Annual Return, Percent			3.02%															0.80%		1.20%
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | IXR6K
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Global Aggregate ex USD ex EM Float Adjusted RIC Diversified Index (Hedged USD)
Average Annual Return, Percent			2.66%																[4]		[4]
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | IXYYF
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Global Aggregate ex-USD Float Adjusted RIC Diversified Index (Hedged USD)
Average Annual Return, Percent			3.00%															0.80%		1.20%
FidelityInternationalBondIndexFund-PRO | Fidelity International Bond Index Fund | LB135
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Global Aggregate Bond Index
Average Annual Return, Percent			8.17%															(2.15%)		(0.27%)
FidelitySAI0-5YearInflation-ProtectedBondIndexFund-PRO | Fidelity SAI 0-5 Year Inflation-Protected Bond Index Fund | Fidelity SAI 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.05%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):	[5]	0.06%
Expenses (as a percentage of Assets)		0.11%
Fee Waiver or Reimbursement	[6]	(0.06%)
Net Expenses (as a percentage of Assets)		0.05%
Expense Example, with Redemption, 1 Year		$ 5
Expense Example, with Redemption, 3 Years		$ 27
FidelitySAI0-5YearInflation-ProtectedBondIndexFund-PRO | Fidelity SAI 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® SAI 0-5 Year Inflation-Protected Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® SAI 0-5 Year Inflation-Protected Bond Index Fund seeks to provide investment results that correspond to the total return of the inflation-protected sector of the United States Treasury market.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Fee Waiver or Reimbursement over Assets, Date of Termination		Apr. 30, 2027
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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. For the period from November 4, 2025 to December 31, 2025, the fund's portfolio turnover rate was 1 % of the average value of its portfolio.
Portfolio Turnover, Rate		1.00%
Other Expenses, New Fund, Based on Estimates [Text]		Based on estimated amounts for the current fiscal year.
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in inflation-protected debt securities included in the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index. The Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index is a market value-weighted index that measures the performance of inflation-protected securities issued by the U.S. Treasury that have a remaining average life of less than 5 years. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index using a smaller number of securities. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		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]		Performance history will be available for the fund after the fund has been in operation for one calendar year.
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.00%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.00%
Expenses (as a percentage of Assets)		0.00%
Expense Example, with Redemption, 1 Year		$ 0
Expense Example, with Redemption, 3 Years		0
Expense Example, with Redemption, 5 Years		0
Expense Example, with Redemption, 10 Years		$ 0
Annual Return, Inception Date		Aug. 13, 2021
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			5.99%															3.14%	[7]
Annual Return [Percent]				5.99%	4.86%	4.65%	(2.84%)
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® Series 0-5 Year Inflation-Protected Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® Series 0-5 Year Inflation-Protected Bond Index Fund seeks to provide investment results that correspond to the total return of the inflation-protected sector of the United States Treasury market.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 38 % of the average value of its portfolio.
Portfolio Turnover, Rate		38.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in inflation-protected debt securities included in the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index. The Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index is a market value-weighted index that measures the performance of inflation-protected securities issued by the U.S. Treasury that have a remaining average life of less than 5 years. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index using a smaller number of securities. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. The performance shown does not reflect the impact of any fees paid at the fee-based account or plan level, if applicable. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Mar. 31, 2025
Highest Quarterly Return		3.00%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Sep. 30, 2022
Lowest Quarterly Return		(2.62%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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.
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund | After Taxes on Distributions | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			4.29%															1.74%	[7]
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund | After Taxes on Distributions and Sales | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			3.54%															1.79%	[7]
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund | LB001
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Aggregate Bond Index
Average Annual Return, Percent			7.30%															(0.23%)
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 0-5 Year Inflation-Protected Bond Index Fund | IXW3Z
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg US Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index
Average Annual Return, Percent			6.07%															3.16%
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.00%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.00%
Expenses (as a percentage of Assets)		0.00%
Expense Example, with Redemption, 1 Year		$ 0
Expense Example, with Redemption, 3 Years		0
Expense Example, with Redemption, 5 Years		0
Expense Example, with Redemption, 10 Years		$ 0
Annual Return, Inception Date		Aug. 13, 2021
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			7.38%															(2.14%)	[8]
Annual Return [Percent]				7.38%	(0.42%)	2.81%	(19.04%)
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® Series 5+ Year Inflation-Protected Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® Series 5+ Year Inflation-Protected Bond Index Fund seeks to provide investment results that correspond to the total return of the inflation-protected sector of the United States Treasury market.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 25 % of the average value of its portfolio.
Portfolio Turnover, Rate		25.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in inflation-protected debt securities included in the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 5+ Years Index. The Bloomberg US Treasury Inflation-Protected Securities (TIPS) 5+ Years Index is a market value-weighted index that measures the performance of inflation-protected securities issued by the U.S. Treasury that have a remaining average life of 5 or more years. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg US Treasury Inflation-Protected Securities (TIPS) 5+ Years Index using a smaller number of securities. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. The performance shown does not reflect the impact of any fees paid at the fee-based account or plan level, if applicable. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Dec. 31, 2023
Highest Quarterly Return		6.31%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Jun. 30, 2022
Lowest Quarterly Return		(10.42%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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.
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund | After Taxes on Distributions | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			5.52%															(3.75%)	[8]
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund | After Taxes on Distributions and Sales | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			4.36%															(2.28%)	[8]
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund | LB001
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Aggregate Bond Index
Average Annual Return, Percent			7.30%															(0.23%)
FidelitySeries0-55YearInflation-ProtectedBondIndexFunds-ComboPRO | Fidelity Series 5+ Year Inflation-Protected Bond Index Fund | IXW40
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg US Treasury Inflation-Protected Securities (TIPS) 5+ Years Index
Average Annual Return, Percent			7.58%															(2.05%)
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund | Fidelity SAI International Credit Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.40%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.02%
Expenses (as a percentage of Assets)		0.42%
Fee Waiver or Reimbursement	[9]	(0.01%)
Net Expenses (as a percentage of Assets)		0.41%
Expense Example, with Redemption, 1 Year		$ 42
Expense Example, with Redemption, 3 Years		134
Expense Example, with Redemption, 5 Years		234
Expense Example, with Redemption, 10 Years		$ 529
Annual Return, Inception Date		Mar. 01, 2023
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			6.40%													6.64%	[10]
Annual Return [Percent]				6.40%	6.19%
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® SAI International Credit Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® SAI International Credit Fund seeks a high level of current income.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Fee Waiver or Reimbursement over Assets, Date of Termination		Apr. 30, 2027
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 55 % of the average value of its portfolio.
Portfolio Turnover, Rate		55.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in debt securities of all types and repurchase agreements for those securities. Debt securities are used by issuers to borrow money. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. Debt securities include corporate bonds, government securities (including Treasury securities), repurchase agreements, money market securities, mortgage and other asset-backed securities, loans and loan participations, and other securities, such as hybrids and synthetic securities, believed to have debt-like characteristics (e.g., securities classified as Tier 2 Regulatory capital, securities that rank above share capital in an insolvency waterfall, securities with maturity dates and non-cancellable interest payment structures).  A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Normally investing primarily in securities of foreign issuers, including securities of issuers located in emerging markets. Emerging markets include countries that have an emerging stock market as defined by MSCI, countries or markets with low- to middle-income economies as classified by the World Bank, and other countries or markets that the Adviser identifies as having similar emerging markets characteristics. The Adviser considers a number of factors to determine whether an issuer is located in or tied economically to a particular country or region including: whether a third-party vendor has assigned a particular country or region classification to the issuer or included the issuer in an index representative of a particular country or region; the issuer's domicile, incorporation, and location of assets; whether the issuer derives at least 50% of its revenues from, or has at least 50% of its assets in, a particular country or region; the source of government guarantees (if any); and the primary trading market or listing exchange. Whether an issuer is located in or tied economically to a particular country can be determined under any of these factors. Normally investing primarily in investment-grade debt securities. Allocating investments across different market sectors, countries, and regions, including the United States. Investing up to 20% of assets in lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds). Hedging the fund's foreign currency exposures utilizing forward foreign currency exchange contracts. Investing in contingent convertible securities. Analyzing the credit quality of the issuer, security-specific features, current and potential future valuation, and trading opportunities to select investments. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default), options, and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Sep. 30, 2024
Highest Quarterly Return		4.98%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Dec. 31, 2024
Lowest Quarterly Return		(0.69%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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.
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund | After Taxes on Distributions | Fidelity SAI International Credit Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			4.65%													4.98%	[10]
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund | After Taxes on Distributions and Sales | Fidelity SAI International Credit Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			3.83%													4.41%	[10]
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund | LB135
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Global Aggregate Bond Index
Average Annual Return, Percent			8.17%													4.32%
FidelitySAIInternationalCreditFund-PRO | Fidelity SAI International Credit Fund | LB427
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Global Aggregate Credit Ex U.S. Index (Hedged USD)
Average Annual Return, Percent			6.36%													6.66%
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund | Fidelity SAI Municipal Income Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.33%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.02%
Expenses (as a percentage of Assets)		0.35%
Expense Example, with Redemption, 1 Year		$ 36
Expense Example, with Redemption, 3 Years		113
Expense Example, with Redemption, 5 Years		197
Expense Example, with Redemption, 10 Years		$ 443
Annual Return, Inception Date		Oct. 02, 2018
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			4.15%															1.00%				2.79%	[11]
Annual Return [Percent]				4.15%	1.83%	7.55%	(9.94%)	2.33%	4.27%	8.51%
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® SAI Municipal Income Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® SAI Municipal Income Fund seeks to provide a high current yield exempt from federal income tax.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 16 % of the average value of its portfolio.
Portfolio Turnover, Rate		16.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in municipal securities whose interest is exempt from federal income tax. The municipal securities in which the fund invests are normally investment-grade (those of medium and high quality). Municipal debt securities are issued to raise money for a variety of public and private purposes, including general financing for state and local governments, financing for eligible non-profit organizations, or financing for a specific project or public facility. Municipal debt securities in which the fund invests include securities issued by U.S. territories and possessions, general obligation bonds of municipalities, local or state governments, project or revenue-specific bonds, or pre-refunded or escrowed bonds, municipal money market securities, and synthetic securities. Municipal securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. Investment grade securities in which the fund invests include securities or issuers rated at least BBB- or its equivalent by at least one nationally recognized statistical ratings organization (NRSRO), or, if unrated, determined by the Adviser to be of comparable quality. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Managing the fund to have similar overall interest rate risk to the supplemental index (see "Additional Index Information" section of the prospectus). Allocating assets across different market sectors and maturities. Potentially investing more than 25% of total assets in municipal securities that finance similar types of projects. Analyzing the credit quality of the issuer, security-specific features, current and potential future valuation, and trading opportunities to select investments.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Dec. 31, 2023
Highest Quarterly Return		8.19%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Mar. 31, 2022
Lowest Quarterly Return		(6.83%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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 Explanation after Tax Higher		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		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. 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.
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund | After Taxes on Distributions | Fidelity SAI Municipal Income Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			4.15%															1.00%				2.74%	[11]
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund | After Taxes on Distributions and Sales | Fidelity SAI Municipal Income Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			3.84%															1.39%				2.78%	[11]
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund | LB083
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg 3+ Year Municipal Bond Index
Average Annual Return, Percent			4.30%															0.69%				2.59%
FidelitySAIMunicipalIncomeFund-PRO | Fidelity SAI Municipal Income Fund | LB015
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg Municipal Bond Index
Average Annual Return, Percent			4.25%															0.80%				2.51%
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund | Fidelity Inflation-Protected Bond Index Fund
Prospectus Line Items
Management Fees (as a percentage of Assets)		0.05%
Distribution and Service (12b-1) Fees		0.00%
Other Expenses (as a percentage of Assets):		0.00%
Expenses (as a percentage of Assets)		0.05%
Expense Example, with Redemption, 1 Year		$ 5
Expense Example, with Redemption, 3 Years		16
Expense Example, with Redemption, 5 Years		28
Expense Example, with Redemption, 10 Years		$ 64
Average Annual Return, Label [Optional Text]			Return Before Taxes
Average Annual Return, Percent			6.79%															1.04%						3.03%
Annual Return [Percent]				6.79%	2.01%	3.78%	(12.05%)	5.93%	10.90%	8.31%	(1.37%)	2.98%	4.88%
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund
Prospectus Line Items
Risk/Return [Heading]		Fund Summary Fund: Fidelity® Inflation-Protected Bond Index Fund
Objective [Heading]		Investment Objective
Objective, Primary [Text Block]		Fidelity® Inflation-Protected Bond Index Fund seeks to provide investment results that correspond to the total return of the inflation-protected sector of the United States Treasury market.
Expense Heading [Optional Text]		Fee Table
Expense Narrative [Text Block]		The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions, which are not reflected in the tables and examples below.
Shareholder Fees Caption [Optional Text]		Shareholder fees
Shareholder Fee, Other		$ 0
Operating Expenses Caption [Optional Text]		Annual Operating Expenses
Portfolio Turnover [Heading]		Portfolio Turnover
Portfolio Turnover [Text Block]		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 19 % of the average value of its portfolio.
Portfolio Turnover, Rate		19.00%
Expense Example Narrative [Text Block]		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 the 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:
Strategy [Heading]		Principal Investment Strategies
Strategy Narrative [Text Block]		Normally investing at least 80% of assets in inflation-protected debt securities included in the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index. The Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index is a market value-weighted index that measures the performance of inflation-protected securities issued by the U.S. Treasury. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index using a smaller number of securities. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
Bar Chart and Performance Table [Heading]		Performance
Performance Narrative [Text Block]		The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. Visit www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text]		The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.
Performance Availability Website Address [Text]		www.fidelity.com
Performance Past Does Not Indicate Future [Text]		Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading]		Year-by-Year Returns
Highest Quarterly Return, Label [Optional Text]		Highest Quarter Return
Highest Quarterly Return, Date		Mar. 31, 2016
Highest Quarterly Return		4.60%
Lowest Quarterly Return, Label [Optional Text]		Lowest Quarter Return
Lowest Quarterly Return, Date		Jun. 30, 2022
Lowest Quarterly Return		(6.19%)
Performance Table Heading		Average Annual Returns
Performance Table Uses Highest Federal Rate		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		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 Explanation after Tax Higher		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		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). 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.
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund | After Taxes on Distributions | Fidelity Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions
Average Annual Return, Percent			5.01%															(0.91%)						1.68%
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund | After Taxes on Distributions and Sales | Fidelity Inflation-Protected Bond Index Fund
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent			4.01%															(0.04%)						1.76%
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund | LB124
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) Index
Average Annual Return, Percent			7.01%															1.12%						3.09%
FidelityInflation-ProtectedBondIndexFund-PRO | Fidelity Inflation-Protected Bond Index Fund | LB001
Prospectus Line Items
Average Annual Return, Label [Optional Text]			Bloomberg U.S. Aggregate Bond Index
Average Annual Return, Percent			7.30%															(0.36%)						2.01%
Document Type		485BPOS
Registrant Name		Fidelity Salem Street Trust

[1] A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.05% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through April 30, 2027 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.

[2] A From August 16, 2024 .

[3] A From October 10, 2019 .

[4] B The inception date for the index was after the fund commenced operations, and returns for this time period are not yet available.

[5] A Based on estimated amounts for the current fiscal year.

[6] B Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.05% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through April 30, 2027 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.

[7] A From August 13, 2021 .

[8] A From August 13, 2021 .

[9] A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.41% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through April 30, 2027 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.

[10] A From March 1, 2023 .

[11] A From October 2, 2018 .