v3.26.3
Shareholder Report
 6 Months Ended
Jul. 31, 2026
USD ($)
shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Fidelity Salem Street Trust
Entity Central Index Key 0000035315
Entity Investment Company Type N-1A
Document Period End Date Jul. 31, 2026
Fidelity Tax-Free Bond Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® Tax-Free Bond Fund
Class Name Fidelity® Tax-Free Bond Fund
Trading Symbol FTABX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Tax-Free Bond Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-8544
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® Tax-Free Bond Fund 
$ 12 
0.25%
  
Expenses Paid, Amount $ 12
Expense Ratio, Percent 0.25%
Net Assets $ 3,826,705,638
Holdings Count | shares 1,269
Investment Company Portfolio Turnover 16.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$3,826,705,638
  
Number of Holdings
1,269
  
Portfolio Turnover
16%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 43.0   Health Care 12.7   Transportation 11.2   Special Tax 8.7   Electric Utilities 6.9   Education 6.2   Others(Individually Less Than 5%) 8.4   97.1       AAA 5.0 AA 41.5 A 38.9 BBB 6.3 BB 1.7 B 0.3 Not Rated 3.4 Short-Term Investments and Net Other Assets (Liabilities) 2.9 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 5.0                                  AA - 41.5                                  A - 38.9                                   BBB - 6.3                                  BB - 1.7                                   B - 0.3                                    Not Rated - 3.4                            Short-Term Investments and Net Other Assets (Liabilities) - 2.9   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Alabama 12.0 Texas 10.3 Illinois 8.9 New York 8.8 Georgia 5.1      
Fidelity Sustainable Intermediate Municipal Income Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity® Sustainable Intermediate Municipal Income Fund
Trading Symbol FSIKX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-8544
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® Sustainable Intermediate Municipal Income Fund 
$ 18 
0.37%
  
Expenses Paid, Amount $ 18
Expense Ratio, Percent 0.37%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Advisor Sustainable Intermediate Municipal Income Fund - Class Z  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity Advisor® Sustainable Intermediate Municipal Income Fund Class Z
Trading Symbol FASVX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-877-208-0098
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Class Z 
$ 15 
0.31%
  
Expenses Paid, Amount $ 15
Expense Ratio, Percent 0.31%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Advisor Sustainable Intermediate Municipal Income Fund - Class M  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity Advisor® Sustainable Intermediate Municipal Income Fund Class M
Trading Symbol FASLX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-877-208-0098
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Class M 
$ 31 
0.62%
  
Expenses Paid, Amount $ 31
Expense Ratio, Percent 0.62%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Advisor Sustainable Intermediate Municipal Income Fund - Class I  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity Advisor® Sustainable Intermediate Municipal Income Fund Class I
Trading Symbol FASUX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-877-208-0098
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Class I 
$ 18 
0.37%
  
Expenses Paid, Amount $ 18
Expense Ratio, Percent 0.37%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Advisor Sustainable Intermediate Municipal Income Fund - Class C  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity Advisor® Sustainable Intermediate Municipal Income Fund Class C
Trading Symbol FASNX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-877-208-0098
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Class C 
$ 67 
1.37%
  
Expenses Paid, Amount $ 67
Expense Ratio, Percent 1.37%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Advisor Sustainable Intermediate Municipal Income Fund - Class A  
Shareholder Report [Line Items]  
Fund Name Fidelity® Sustainable Intermediate Municipal Income Fund
Class Name Fidelity Advisor® Sustainable Intermediate Municipal Income Fund Class A
Trading Symbol FASJX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Sustainable Intermediate Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-877-208-0098
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Class A 
$ 31 
0.62%
  
Expenses Paid, Amount $ 31
Expense Ratio, Percent 0.62%
Net Assets $ 25,420,925
Holdings Count | shares 273
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$25,420,925
  
Number of Holdings
273
  
Portfolio Turnover
37%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 39.9   Housing 15.4   Health Care 11.1   Education 10.2   Electric Utilities 5.5   Special Tax 5.3   Water & Sewer 5.3   Others(Individually Less Than 5%) 7.4   100.1       AAA 15.0 AA 51.2 A 26.2 BBB 5.7 BB 1.4 Not Rated 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 15.0                                 AA - 51.2                                  A - 26.2                                   BBB - 5.7                                  BB - 1.4                                   Not Rated - 0.6                          Short-Term Investments and Net Other Assets (Liabilities) - (0.1)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.7 Alabama 12.0 California 7.7 Georgia 6.2 New York 5.4      
Fidelity Series Large Cap Value Index Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® Series Large Cap Value Index Fund
Class Name Fidelity® Series Large Cap Value Index Fund
Trading Symbol FIOOX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Series Large Cap Value Index Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544.
Additional Information Phone Number 1-800-544-8544
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® Series Large Cap Value Index Fund 
$ 0 A
0.00%B
  
AAmount represents less than $.50
BAmount represents less than 0.005%
 
Expenses Paid, Amount $ 0
Expense Ratio, Percent 0.00%
Net Assets $ 12,008,713,126
Holdings Count | shares 874
Investment Company Portfolio Turnover 55.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$12,008,713,126
  
Number of Holdings
874
  
Portfolio Turnover
55%
  
Holdings [Text Block]       MARKET SECTORS (% of Fund's net assets)     Financials 19.4   Information Technology 18.3   Health Care 12.6   Industrials 11.1   Consumer Discretionary 11.0   Consumer Staples 7.3   Energy 5.9   Utilities 3.7   Real Estate 3.6   Materials 3.6   Communication Services 3.2     Common Stocks 99.7 Short-Term Investments and Net Other Assets (Liabilities) 0.3 ASSET ALLOCATION (% of Fund's net assets)     Common Stocks - 99.7                       Short-Term Investments and Net Other Assets (Liabilities) - 0.3   United States 99.8 Canada 0.2 United Kingdom 0.0 Australia 0.0 Bermuda 0.0 Mexico 0.0 Puerto Rico 0.0 Guatemala 0.0 Brazil 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets)     United States - 99.8                       Canada - 0.2                               United Kingdom - 0.0                       Australia - 0.0                            Bermuda - 0.0                              Mexico - 0.0                               Puerto Rico - 0.0                          Guatemala - 0.0                            Brazil - 0.0                                  
Largest Holdings [Text Block] TOP HOLDINGS(% of Fund's net assets)     Amazon.com Inc 6.6   Apple Inc 5.5   Microsoft Corp 4.8   Berkshire Hathaway Inc Class B 2.7   JPMorgan Chase & Co 2.6   ExxonMobil Holdings Corp 1.8   Johnson & Johnson 1.7   Cisco Systems Inc 1.2   Walmart Inc 1.2   AbbVie Inc 1.1     29.2  
Fidelity SAI Tax-Free Bond Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® SAI Tax-Free Bond Fund
Class Name Fidelity® SAI Tax-Free Bond Fund
Trading Symbol FSAJX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® SAI Tax-Free Bond Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-3455 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-3455
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® SAI Tax-Free Bond Fund 
$ 12 
0.25%
  
Expenses Paid, Amount $ 12
Expense Ratio, Percent 0.25%
Net Assets $ 5,931,905,029
Holdings Count | shares 1,828
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$5,931,905,029
  
Number of Holdings
1,828
  
Portfolio Turnover
19%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 44.0   Health Care 12.1   Special Tax 9.5   Electric Utilities 7.2   Transportation 6.8   Housing 6.5   Water & Sewer 5.9   Others(Individually Less Than 5%) 6.2   98.2       AAA 6.4 AA 50.0 A 33.4 BBB 4.4 BB 0.9 B 0.1 Not Rated 3.0 Short-Term Investments and Net Other Assets (Liabilities) 1.8 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 6.4                                  AA - 50.0                                  A - 33.4                                   BBB - 4.4                                  BB - 0.9                                   B - 0.1                                    Not Rated - 3.0                            Short-Term Investments and Net Other Assets (Liabilities) - 1.8   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 12.9 New York 12.5 Alabama 11.0 Illinois 7.3 Georgia 4.9      
Fidelity SAI Sustainable Municipal Income Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® SAI Sustainable Municipal Income Fund
Class Name Fidelity® SAI Sustainable Municipal Income Fund
Trading Symbol FASWX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® SAI Sustainable Municipal Income Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-3455 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-3455
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® SAI Sustainable Municipal Income Fund 
$ 18 
0.36%
  
Expenses Paid, Amount $ 18
Expense Ratio, Percent 0.36%
Net Assets $ 97,430,869
Holdings Count | shares 433
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$97,430,869
  
Number of Holdings
433
  
Portfolio Turnover
22%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 33.8   Health Care 18.4   Housing 14.7   Education 12.2   Water & Sewer 8.4   Electric Utilities 6.3   Others(Individually Less Than 5%) 7.0   100.8       AAA 11.6 AA 57.1 A 25.9 BBB 5.9 BB 0.1 Not Rated 0.2 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 11.6                                 AA - 57.1                                  A - 25.9                                   BBB - 5.9                                  BB - 0.1                                   Not Rated - 0.2                          Short-Term Investments and Net Other Assets (Liabilities) - (0.8)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Alabama 12.9 Texas 10.1 New York 9.4 Georgia 6.2 Illinois 4.6      
Fidelity SAI Sustainable Conservative Income Municipal Bond Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® SAI Sustainable Conservative Income Municipal Bond Fund
Class Name Fidelity® SAI Sustainable Conservative Income Municipal Bond Fund
Trading Symbol FASYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® SAI Sustainable Conservative Income Municipal Bond Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-3455 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-3455
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® SAI Sustainable Conservative Income Municipal Bond Fund 
$ 10 
0.20%
  
Expenses Paid, Amount $ 10
Expense Ratio, Percent 0.20%
Net Assets $ 27,325,773
Holdings Count | shares 139
Investment Company Portfolio Turnover 67.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$27,325,773
  
Number of Holdings
139
  
Portfolio Turnover
67%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 21.4   Health Care 15.0   Electric Utilities 14.9   Resource Recovery 14.8   Housing 12.2   Industrial Development 8.4   Synthetics 5.1   Others(Individually Less Than 5%) 6.7   98.5       AAA 5.2 AA 33.6 A 54.1 BBB 0.5 Not Rated 5.1 Short-Term Investments and Net Other Assets (Liabilities) 1.5 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 5.2                                  AA - 33.6                                  A - 54.1                                   BBB - 0.5                                  Not Rated - 5.1                            Short-Term Investments and Net Other Assets (Liabilities) - 1.5   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Alabama 9.2 Florida 8.7 California 8.7 Georgia 8.1 Texas 7.6      
Fidelity SAI Conservative Income Municipal Bond Fund  
Shareholder Report [Line Items]  
Fund Name Fidelity® SAI Conservative Income Municipal Bond Fund
Class Name Fidelity® SAI Conservative Income Municipal Bond Fund
Trading Symbol FSMJX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® SAI Conservative Income Municipal Bond Fund for the period February 1, 2026 to July 31, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-3455 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-3455
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® SAI Conservative Income Municipal Bond Fund 
$ 10 
0.20%
  
Expenses Paid, Amount $ 10
Expense Ratio, Percent 0.20%
Net Assets $ 1,604,430,742
Holdings Count | shares 451
Investment Company Portfolio Turnover 81.00%
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of July 31, 2026)
 
KEY FACTS 
  
  
Fund Size
$1,604,430,742
  
Number of Holdings
451
  
Portfolio Turnover
81%
  
Holdings [Text Block]   REVENUE SOURCES (% of Fund's net assets) General Obligations 26.2   Synthetics 17.9   Resource Recovery 11.1   Industrial Development 9.3   Transportation 8.6   Health Care 8.4   Housing 8.2   Electric Utilities 7.1   Others(Individually Less Than 5%) 4.2   101.0       AAA 4.3 AA 31.6 A 44.5 BBB 6.1 Not Rated 14.3 QUALITY DIVERSIFICATION (% of Fund's net assets)     AAA - 4.3                                  AA - 31.6                                  A - 44.5                                   BBB - 6.1                                  Not Rated - 14.3                         Short-Term Investments and Net Other Assets (Liabilities) - (0.8)%   We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes.       TOP STATES (% of Fund's net assets) Texas 15.0 New York 12.0 California 8.5 Alabama 7.0 Florida 6.4