| Form N-CSR Cover | 6 Months Ended |
| Dec. 31, 2024 | |
| 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 | Dec. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Dec. 31, 2024 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 | Dec. 31, 2024 |
| Fidelity Small Cap Growth Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Small Cap Growth Index Fund |
| Class Name | Fidelity® Small Cap Growth Index Fund |
| Trading Symbol | FECGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Small Cap Growth Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Small Cap Growth Index Fund $ 0.05 % |
| Expenses Paid, Amount | $ 3 |
| Expense Ratio, Percent | 0.05% |
| Net Assets | $ 839,605,762 |
| Holdings Count | shares | 1,129 |
| Investment Company Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,129 Portfolio Turnover 13 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Health Care 23.5 Industrials 22.6 Information Technology 20.9 Consumer Discretionary 10.1 Financials 8.5 Materials 3.7 Consumer Staples 3.4 Energy 3.2 Communication Services 2.1 Real Estate 1.4 Utilities 0.4 Common Stocks 99.8 Short-Term Investments and Net Other Assets (Liabilities) 0.2 ASSET ALLOCATION (% of Fund's net assets) Common Stocks - 99.8 Short-Term Investments and Net Other Assets (Liabilities) - 0.2 United States 97.6 Thailand 0.7 Canada 0.3 Singapore 0.3 Puerto Rico 0.2 India 0.1 Bahamas (Nassau) 0.1 Brazil 0.1 Ghana 0.1 Others 0.5 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) United States - 97.6 Thailand - 0.7 Canada - 0.3 Singapore - 0.3 Puerto Rico - 0.2 India - 0.1 Bahamas (Nassau) - 0.1 Brazil - 0.1 Ghana - 0.1 Others - 0.5 |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) FTAI Aviation Ltd 1.1 Sprouts Farmers Market Inc 1.0 Insmed Inc 1.0 Vaxcyte Inc 0.8 Credo Technology Group Holding Ltd 0.8 Applied Industrial Technologies Inc 0.7 Rocket Lab USA Inc Class A 0.7 IonQ Inc 0.7 HealthEquity Inc 0.7 Mueller Industries Inc 0.7 8.2 |
| Fidelity Small Cap Value Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Small Cap Value Index Fund |
| Class Name | Fidelity® Small Cap Value Index Fund |
| Trading Symbol | FISVX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Small Cap Value Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Small Cap Value Index Fund $ 0.05 % |
| Expenses Paid, Amount | $ 3 |
| Expense Ratio, Percent | 0.05% |
| Net Assets | $ 1,313,781,363 |
| Holdings Count | shares | 1,449 |
| Investment Company Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,449 Portfolio Turnover 13 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 29.2 Industrials 12.6 Real Estate 11.0 Consumer Discretionary 9.2 Health Care 8.7 Energy 7.1 Information Technology 6.5 Utilities 5.2 Materials 4.8 Communication Services 3.1 Consumer Staples 2.3 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 96.4 Canada 1.0 Argentina 0.5 Puerto Rico 0.4 Norway 0.4 Cameroon 0.3 Monaco 0.2 Bermuda 0.2 Brazil 0.1 Others 0.5 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) United States - 96.4 Canada - 1.0 Argentina - 0.5 Puerto Rico - 0.4 Norway - 0.4 Cameroon - 0.3 Monaco - 0.2 Bermuda - 0.2 Brazil - 0.1 Others - 0.5 |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) SouthState Corp 0.7 Old National Bancorp/IN 0.6 Jackson Financial Inc 0.6 Cadence Bank 0.6 Taylor Morrison Home Corp 0.6 Summit Materials Inc Class A 0.5 Glacier Bancorp Inc 0.5 Commercial Metals Co 0.5 Terreno Realty Corp 0.4 Essent Group Ltd 0.4 5.4 |
| Fidelity SAI Municipal Bond Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® SAI Municipal Bond Index Fund |
| Class Name | Fidelity® SAI Municipal Bond Index Fund |
| Trading Symbol | FSABX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® SAI Municipal Bond Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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 Municipal Bond Index Fund $ 0.07 % |
| Expenses Paid, Amount | $ 4 |
| Expense Ratio, Percent | 0.07% |
| Net Assets | $ 81,891,847 |
| Holdings Count | shares | 1,242 |
| Investment Company Portfolio Turnover | 19% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,242 Portfolio Turnover 19 % |
| Holdings [Text Block] | REVENUE SOURCES (% of Fund's net assets) General Obligations 35.0 Transportation 15.4 Special Tax 15.2 Water & Sewer 9.3 Health Care 8.4 Electric Utilities 6.0 Education 5.8 Others(Individually Less Than 5%) 4.9 100.0 AAA 16.5 AA 57.0 A 22.0 BBB 3.9 B 0.0 Not Rated 0.8 QUALITY DIVERSIFICATION (% of Fund's net assets) AAA - 16.5 AA - 57.0 A - 22.0 BBB - 3.9 B - 0.0 Not Rated - 0.8 Short-Term Investments and Net Other Assets (Liabilities) - (0.2)% 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) California 19.0 New York 19.0 Texas 8.4 Illinois 4.5 Washington 4.1 |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Municipal Income 2025 Fund |
| Class Name | Fidelity Advisor® Municipal Income 2025 Fund Class A |
| Trading Symbol | FAMHX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Municipal Income 2025 Fund for the period July 1, 2024 to December 31, 2024. |
| 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 $ 0.65 % |
| Expenses Paid, Amount | $ 33 |
| Expense Ratio, Percent | 0.65% |
| Net Assets | $ 22,111,435 |
| Holdings Count | shares | 118 |
| Investment Company Portfolio Turnover | 0% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 118 Portfolio Turnover 0 % |
| Holdings [Text Block] | REVENUE SOURCES (% of Fund's net assets) Health Care 27.4 Transportation 24.9 Education 22.0 General Obligations 11.0 Housing 5.7 Others(Individually Less Than 5%) 9.0 100.0 AAA 9.8 AA 23.6 A 41.8 BBB 16.6 BB 3.1 B 0.5 Not Rated 4.0 Short-Term Investments and Net Other Assets (Liabilities) 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets) AAA - 9.8 AA - 23.6 A - 41.8 BBB - 16.6 BB - 3.1 B - 0.5 Not Rated - 4.0 Short-Term Investments and Net Other Assets (Liabilities) - 0.6 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) Connecticut 11.8 Pennsylvania 10.0 Illinois 8.2 Massachusetts 6.2 Ohio 5.4 |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Municipal Income 2025 Fund |
| Class Name | Fidelity Advisor® Municipal Income 2025 Fund Class I |
| Trading Symbol | FAMYX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Municipal Income 2025 Fund for the period July 1, 2024 to December 31, 2024. |
| 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 $ 0.40 % |
| Expenses Paid, Amount | $ 20 |
| Expense Ratio, Percent | 0.40% |
| Net Assets | $ 22,111,435 |
| Holdings Count | shares | 118 |
| Investment Company Portfolio Turnover | 0% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 118 Portfolio Turnover 0 % |
| Holdings [Text Block] | REVENUE SOURCES (% of Fund's net assets) Health Care 27.4 Transportation 24.9 Education 22.0 General Obligations 11.0 Housing 5.7 Others(Individually Less Than 5%) 9.0 100.0 AAA 9.8 AA 23.6 A 41.8 BBB 16.6 BB 3.1 B 0.5 Not Rated 4.0 Short-Term Investments and Net Other Assets (Liabilities) 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets) AAA - 9.8 AA - 23.6 A - 41.8 BBB - 16.6 BB - 3.1 B - 0.5 Not Rated - 4.0 Short-Term Investments and Net Other Assets (Liabilities) - 0.6 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) Connecticut 11.8 Pennsylvania 10.0 Illinois 8.2 Massachusetts 6.2 Ohio 5.4 |
| Fidelity Mid Cap Growth Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Mid Cap Growth Index Fund |
| Class Name | Fidelity® Mid Cap Growth Index Fund |
| Trading Symbol | FMDGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Mid Cap Growth Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Mid Cap Growth Index Fund $ 0.05 % |
| Expenses Paid, Amount | $ 3 |
| Expense Ratio, Percent | 0.05% |
| Net Assets | $ 1,555,968,229 |
| Holdings Count | shares | 294 |
| Investment Company Portfolio Turnover | 10% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 294 Portfolio Turnover 10 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 27.4 Industrials 17.3 Consumer Discretionary 14.7 Financials 12.8 Health Care 12.5 Communication Services 4.5 Energy 4.0 Consumer Staples 2.3 Utilities 1.8 Real Estate 1.3 Materials 1.1 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 98.1 Brazil 1.1 Korea (South) 0.8 Puerto Rico 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) United States - 98.1 Brazil - 1.1 Korea (South) - 0.8 Puerto Rico - 0.0 |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Palantir Technologies Inc Class A 5.1 AppLovin Corp Class A 2.8 Trade Desk Inc (The) Class A 1.7 Ameriprise Financial Inc 1.6 Vistra Corp 1.6 Datadog Inc Class A 1.4 Axon Enterprise Inc 1.4 Coinbase Global Inc Class A 1.4 Vertiv Holdings Co Class A 1.4 Fair Isaac Corp 1.3 19.7 |
| Fidelity Mid Cap Value Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Mid Cap Value Index Fund |
| Class Name | Fidelity® Mid Cap Value Index Fund |
| Trading Symbol | FIMVX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Mid Cap Value Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Mid Cap Value Index Fund $ 0.05 % |
| Expenses Paid, Amount | $ 3 |
| Expense Ratio, Percent | 0.05% |
| Net Assets | $ 949,777,691 |
| Holdings Count | shares | 716 |
| Investment Company Portfolio Turnover | 25% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 716 Portfolio Turnover 25 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 18.0 Industrials 17.1 Real Estate 9.8 Consumer Discretionary 9.3 Information Technology 9.1 Health Care 8.2 Utilities 6.9 Materials 6.7 Energy 5.7 Consumer Staples 5.7 Communication Services 3.3 Common Stocks 99.8 Short-Term Investments and Net Other Assets (Liabilities) 0.2 ASSET ALLOCATION (% of Fund's net assets) Common Stocks - 99.8 Short-Term Investments and Net Other Assets (Liabilities) - 0.2 United States 99.1 Canada 0.3 Bailiwick Of Jersey 0.3 Bermuda 0.1 United Kingdom 0.1 Puerto Rico 0.1 Brazil 0.0 Belgium 0.0 Japan 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) United States - 99.1 Canada - 0.3 Bailiwick Of Jersey - 0.3 Bermuda - 0.1 United Kingdom - 0.1 Puerto Rico - 0.1 Brazil - 0.0 Belgium - 0.0 Japan - 0.0 |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Williams Cos Inc/The 0.8 Arthur J Gallagher & Co 0.7 Digital Realty Trust Inc 0.7 ONEOK Inc 0.7 AFLAC Inc 0.7 Bank of New York Mellon Corp/The 0.7 Kinder Morgan Inc 0.6 Cummins Inc 0.5 Realty Income Corp 0.5 MicroStrategy Inc Class A 0.5 6.4 |
| Fidelity Municipal Income 2025 Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Municipal Income 2025 Fund |
| Class Name | Fidelity® Municipal Income 2025 Fund |
| Trading Symbol | FIMSX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Municipal Income 2025 Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Municipal Income 2025 Fund $ 0.40 % |
| Expenses Paid, Amount | $ 20 |
| Expense Ratio, Percent | 0.40% |
| Net Assets | $ 22,111,435 |
| Holdings Count | shares | 118 |
| Investment Company Portfolio Turnover | 0% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 118 Portfolio Turnover 0 % |
| Holdings [Text Block] | REVENUE SOURCES (% of Fund's net assets) Health Care 27.4 Transportation 24.9 Education 22.0 General Obligations 11.0 Housing 5.7 Others(Individually Less Than 5%) 9.0 100.0 AAA 9.8 AA 23.6 A 41.8 BBB 16.6 BB 3.1 B 0.5 Not Rated 4.0 Short-Term Investments and Net Other Assets (Liabilities) 0.6 QUALITY DIVERSIFICATION (% of Fund's net assets) AAA - 9.8 AA - 23.6 A - 41.8 BBB - 16.6 BB - 3.1 B - 0.5 Not Rated - 4.0 Short-Term Investments and Net Other Assets (Liabilities) - 0.6 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) Connecticut 11.8 Pennsylvania 10.0 Illinois 8.2 Massachusetts 6.2 Ohio 5.4 |
| Fidelity Municipal Bond Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Municipal Bond Index Fund |
| Class Name | Fidelity® Municipal Bond Index Fund |
| Trading Symbol | FMBIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Municipal Bond Index Fund for the period July 1, 2024 to December 31, 2024. |
| 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® Municipal Bond Index Fund $ 0.07 % |
| Expenses Paid, Amount | $ 4 |
| Expense Ratio, Percent | 0.07% |
| Net Assets | $ 178,603,670 |
| Holdings Count | shares | 1,757 |
| Investment Company Portfolio Turnover | 14% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of December 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,757 Portfolio Turnover 14 % |
| Holdings [Text Block] | REVENUE SOURCES (% of Fund's net assets) General Obligations 36.7 Transportation 15.0 Special Tax 12.6 Water & Sewer 9.7 Health Care 8.2 Education 6.5 Others(Individually Less Than 5%) 11.3 100.0 AAA 17.5 AA 55.5 A 22.1 BBB 3.7 BB 0.0 B 0.0 Not Rated 0.8 Short-Term Investments and Net Other Assets (Liabilities) 0.4 QUALITY DIVERSIFICATION (% of Fund's net assets) AAA - 17.5 AA - 55.5 A - 22.1 BBB - 3.7 BB - 0.0 B - 0.0 Not Rated - 0.8 Short-Term Investments and Net Other Assets (Liabilities) - 0.4 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) California 21.8 New York 16.9 Texas 8.2 Florida 4.2 Illinois 4.1 |
| Shareholder Report, Holdings (Details) | Dec. 31, 2024 |
| Fidelity Small Cap Growth Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Fidelity Small Cap Growth Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Small Cap Growth Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Small Cap Growth Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Small Cap Growth Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Small Cap Growth Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.50% |
| Fidelity Small Cap Growth Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.90% |
| Fidelity Small Cap Growth Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.50% |
| Fidelity Small Cap Growth Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Small Cap Growth Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.60% |
| Fidelity Small Cap Growth Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity Small Cap Growth Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.10% |
| Fidelity Small Cap Growth Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Fidelity Small Cap Growth Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Fidelity Small Cap Growth Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| Fidelity Small Cap Growth Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Growth Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.60% |
| Fidelity Small Cap Growth Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Growth Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Growth Index Fund | Singapore | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Growth Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Growth Index Fund | India | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Growth Index Fund | BahamasNassauMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Growth Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Growth Index Fund | Ghana | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Growth Index Fund | OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Growth Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.80% |
| Fidelity Small Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Value Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Small Cap Value Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Value Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Value Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Value Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Value Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Value Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Value Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Value Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Value Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Value Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 29.20% |
| Fidelity Small Cap Value Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| Fidelity Small Cap Value Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| Fidelity Small Cap Value Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| Fidelity Small Cap Value Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.60% |
| Fidelity Small Cap Value Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| Fidelity Small Cap Value Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.20% |
| Fidelity Small Cap Value Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Small Cap Value Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Small Cap Value Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| Fidelity Small Cap Value Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Fidelity Small Cap Value Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 96.40% |
| Fidelity Small Cap Value Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Small Cap Value Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Value Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Value Index Fund | OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Value Index Fund | Argentina | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Value Index Fund | Norway | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Value Index Fund | Cameroon | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Value Index Fund | Monaco | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Value Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Value Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Small Cap Value Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity SAI Municipal Bond Index Fund | TS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19% |
| Fidelity SAI Municipal Bond Index Fund | TS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19% |
| Fidelity SAI Municipal Bond Index Fund | TS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| Fidelity SAI Municipal Bond Index Fund | TS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| Fidelity SAI Municipal Bond Index Fund | TS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| Fidelity SAI Municipal Bond Index Fund | RS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 35% |
| Fidelity SAI Municipal Bond Index Fund | RS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.40% |
| Fidelity SAI Municipal Bond Index Fund | RS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.20% |
| Fidelity SAI Municipal Bond Index Fund | RS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.30% |
| Fidelity SAI Municipal Bond Index Fund | RS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| Fidelity SAI Municipal Bond Index Fund | RS5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6% |
| Fidelity SAI Municipal Bond Index Fund | RS6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| Fidelity SAI Municipal Bond Index Fund | RS7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| Fidelity SAI Municipal Bond Index Fund | QDAAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.50% |
| Fidelity SAI Municipal Bond Index Fund | QDAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 57% |
| Fidelity SAI Municipal Bond Index Fund | QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22% |
| Fidelity SAI Municipal Bond Index Fund | QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Fidelity SAI Municipal Bond Index Fund | QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity SAI Municipal Bond Index Fund | QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | TS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | TS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | TS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | TS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | TS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.40% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.90% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | RS5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDAAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.60% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.60% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Advisor Municipal Income 2025 Fund - Class A | QDShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | TS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | TS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | TS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | TS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | TS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.40% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.90% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | RS5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDAAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.60% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.60% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Advisor Municipal Income 2025 Fund - Class I | QDShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Mid Cap Growth Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| Fidelity Mid Cap Growth Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Fidelity Mid Cap Growth Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity Mid Cap Growth Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity Mid Cap Growth Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity Mid Cap Growth Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Mid Cap Growth Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Mid Cap Growth Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Mid Cap Growth Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Mid Cap Growth Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity Mid Cap Growth Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| Fidelity Mid Cap Growth Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.40% |
| Fidelity Mid Cap Growth Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.50% |
| Fidelity Mid Cap Growth Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity Mid Cap Growth Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.30% |
| Fidelity Mid Cap Growth Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Fidelity Mid Cap Growth Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.70% |
| Fidelity Mid Cap Growth Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Mid Cap Growth Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| Fidelity Mid Cap Growth Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Fidelity Mid Cap Growth Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| Fidelity Mid Cap Growth Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 98.10% |
| Fidelity Mid Cap Growth Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Growth Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Fidelity Mid Cap Growth Index Fund | Korea, Republic of | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Mid Cap Growth Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Mid Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Mid Cap Value Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Mid Cap Value Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Mid Cap Value Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Mid Cap Value Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Mid Cap Value Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Mid Cap Value Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Mid Cap Value Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Mid Cap Value Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Value Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Value Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Value Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18% |
| Fidelity Mid Cap Value Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.10% |
| Fidelity Mid Cap Value Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Mid Cap Value Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Mid Cap Value Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.10% |
| Fidelity Mid Cap Value Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.70% |
| Fidelity Mid Cap Value Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.30% |
| Fidelity Mid Cap Value Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Mid Cap Value Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| Fidelity Mid Cap Value Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Mid Cap Value Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.90% |
| Fidelity Mid Cap Value Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.10% |
| Fidelity Mid Cap Value Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Mid Cap Value Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Value Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Value Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Value Index Fund | BailiwickOfJerseyMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Mid Cap Value Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Value Index Fund | Belgium | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Value Index Fund | Japan | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Value Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.80% |
| Fidelity Mid Cap Value Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Municipal Income 2025 Fund | TS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| Fidelity Municipal Income 2025 Fund | TS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Fidelity Municipal Income 2025 Fund | TS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Municipal Income 2025 Fund | TS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Municipal Income 2025 Fund | TS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| Fidelity Municipal Income 2025 Fund | RS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.40% |
| Fidelity Municipal Income 2025 Fund | RS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.90% |
| Fidelity Municipal Income 2025 Fund | RS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22% |
| Fidelity Municipal Income 2025 Fund | RS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| Fidelity Municipal Income 2025 Fund | RS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Municipal Income 2025 Fund | RS5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9% |
| Fidelity Municipal Income 2025 Fund | QDAAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Municipal Income 2025 Fund | QDAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.60% |
| Fidelity Municipal Income 2025 Fund | QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| Fidelity Municipal Income 2025 Fund | QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.60% |
| Fidelity Municipal Income 2025 Fund | QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Municipal Income 2025 Fund | QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Fidelity Municipal Income 2025 Fund | QDBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Municipal Income 2025 Fund | QDShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Municipal Bond Index Fund | TS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.80% |
| Fidelity Municipal Bond Index Fund | TS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.90% |
| Fidelity Municipal Bond Index Fund | TS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Municipal Bond Index Fund | TS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.20% |
| Fidelity Municipal Bond Index Fund | TS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| Fidelity Municipal Bond Index Fund | RS0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 36.70% |
| Fidelity Municipal Bond Index Fund | RS1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15% |
| Fidelity Municipal Bond Index Fund | RS2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.60% |
| Fidelity Municipal Bond Index Fund | RS3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity Municipal Bond Index Fund | RS4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| Fidelity Municipal Bond Index Fund | RS5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| Fidelity Municipal Bond Index Fund | RS6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity Municipal Bond Index Fund | QDAAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.50% |
| Fidelity Municipal Bond Index Fund | QDAAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 55.50% |
| Fidelity Municipal Bond Index Fund | QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.10% |
| Fidelity Municipal Bond Index Fund | QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity Municipal Bond Index Fund | QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Municipal Bond Index Fund | QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Municipal Bond Index Fund | QDBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Municipal Bond Index Fund | QDShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
