| Form N-CSR Cover | 6 Months Ended |
| Oct. 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 | Oct. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Oct. 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 | Oct. 31, 2024 |
| Fidelity Flex Mid Cap Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity Flex® Mid Cap Index Fund |
| Class Name | Fidelity Flex® Mid Cap Index Fund |
| Trading Symbol | FLAPX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity Flex® Mid Cap Index Fund for the period May 1, 2024 to October 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 Flex® Mid Cap Index Fund $ A 0.00 % B A Amount represents less than $.50 B Amount represents less than 0.005% |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0% |
| Net Assets | $ 458,809,372 |
| Holdings Count | shares | 816 |
| Investment Company Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 816 Portfolio Turnover 29 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Industrials 17.5 Financials 16.2 Information Technology 12.5 Consumer Discretionary 10.6 Health Care 9.7 Real Estate 7.9 Materials 5.9 Utilities 5.7 Energy 5.2 Consumer Staples 4.9 Communication Services 3.6 Common Stocks 99.7 Preferred Stocks 0.0 Short-Term Investments and Net Other Assets (Liabilities) 0.3 ASSET ALLOCATION (% of Fund's net assets) United States 98.7 Brazil 0.5 Korea (South) 0.3 Canada 0.1 Bermuda 0.1 United Kingdom 0.1 Belgium 0.1 Puerto Rico 0.1 Japan 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Palantir Technologies Inc Class A 0.8 Digital Realty Trust Inc 0.6 Williams Cos Inc/The 0.5 Arthur J Gallagher & Co 0.5 AFLAC Inc 0.5 Hilton Worldwide Holdings Inc 0.5 ONEOK Inc 0.5 Bank of New York Mellon Corp/The 0.5 Simon Property Group Inc 0.5 United Rentals Inc 0.5 5.4 |
| Fidelity Series Large Cap Growth Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Series Large Cap Growth Index Fund |
| Class Name | Fidelity® Series Large Cap Growth Index Fund |
| Trading Symbol | FHOFX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Series Large Cap Growth Index Fund for the period May 1, 2024 to October 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. |
| 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 Growth Index Fund $ A 0.00 % B A Amount represents less than $.50 B Amount represents less than 0.005% |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0% |
| Net Assets | $ 1,488,228,107 |
| Holdings Count | shares | 399 |
| Investment Company Portfolio Turnover | 43% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 399 Portfolio Turnover 43 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 48.7 Consumer Discretionary 14.1 Communication Services 13.1 Health Care 7.5 Financials 6.6 Industrials 4.6 Consumer Staples 3.5 Materials 0.6 Real Estate 0.6 Energy 0.4 Utilities 0.2 Common Stocks 99.9 Short-Term Investments and Net Other Assets (Liabilities) 0.1 ASSET ALLOCATION (% of Fund's net assets) United States 99.7 Brazil 0.2 Korea (South) 0.1 Mexico 0.0 Puerto Rico 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 12.0 NVIDIA Corp 11.3 Microsoft Corp 11.1 Amazon.com Inc 6.4 Meta Platforms Inc Class A 4.5 Alphabet Inc Class A 3.7 Alphabet Inc Class C 3.1 Broadcom Inc 2.8 Tesla Inc 2.6 Eli Lilly & Co 2.5 60.0 |
| Fidelity Large Cap Growth Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Large Cap Growth Index Fund |
| Class Name | Fidelity® Large Cap Growth Index Fund |
| Trading Symbol | FSPGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Large Cap Growth Index Fund for the period May 1, 2024 to October 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® Large Cap Growth Index Fund $ 0.03 % |
| Expenses Paid, Amount | $ 2 |
| Expense Ratio, Percent | 0.03% |
| Net Assets | $ 28,433,616,039 |
| Holdings Count | shares | 399 |
| Investment Company Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 399 Portfolio Turnover 13 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 48.5 Consumer Discretionary 14.1 Communication Services 13.1 Health Care 7.5 Financials 6.6 Industrials 4.6 Consumer Staples 3.5 Materials 0.6 Real Estate 0.6 Energy 0.4 Utilities 0.2 Common Stocks 99.7 Short-Term Investments and Net Other Assets (Liabilities) 0.3 ASSET ALLOCATION (% of Fund's net assets) United States 99.7 Brazil 0.2 Korea (South) 0.1 Mexico 0.0 Puerto Rico 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 12.0 NVIDIA Corp 11.3 Microsoft Corp 11.1 Amazon.com Inc 6.4 Meta Platforms Inc Class A 4.5 Alphabet Inc Class A 3.7 Alphabet Inc Class C 3.0 Broadcom Inc 2.8 Tesla Inc 2.6 Eli Lilly & Co 2.5 59.9 |
| Fidelity Flex Small Cap Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity Flex® Small Cap Index Fund |
| Class Name | Fidelity Flex® Small Cap Index Fund |
| Trading Symbol | FLXSX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity Flex® Small Cap Index Fund for the period May 1, 2024 to October 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 Flex® Small Cap Index Fund $ A 0.00 % B A Amount represents less than $.50 B Amount represents less than 0.005% |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0% |
| Net Assets | $ 423,819,778 |
| Holdings Count | shares | 1,982 |
| Investment Company Portfolio Turnover | 15% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,982 Portfolio Turnover 15 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 18.6 Health Care 17.2 Industrials 17.0 Information Technology 12.6 Consumer Discretionary 9.7 Real Estate 6.3 Energy 5.1 Materials 4.6 Utilities 2.9 Consumer Staples 2.7 Communication Services 2.6 Common Stocks 99.3 Short-Term Investments and Net Other Assets (Liabilities) 0.7 ASSET ALLOCATION (% of Fund's net assets) United States 97.1 Canada 0.6 Thailand 0.3 Puerto Rico 0.3 Argentina 0.3 Norway 0.2 Brazil 0.2 Cameroon 0.1 Monaco 0.1 Others 0.8 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) FTAI Aviation Ltd 0.6 Vaxcyte Inc 0.6 Sprouts Farmers Market Inc 0.5 Insmed Inc 0.5 Mueller Industries Inc 0.4 Fluor Corp 0.4 Applied Industrial Technologies Inc 0.4 Ensign Group Inc/The 0.4 REVOLUTION Medicines Inc 0.4 Jackson Financial Inc 0.4 4.6 |
| Fidelity Large Cap Value Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Large Cap Value Index Fund |
| Class Name | Fidelity® Large Cap Value Index Fund |
| Trading Symbol | FLCOX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Large Cap Value Index Fund for the period May 1, 2024 to October 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® Large Cap Value Index Fund $ 0.03 % |
| Expenses Paid, Amount | $ 2 |
| Expense Ratio, Percent | 0.03% |
| Net Assets | $ 9,285,824,297 |
| Holdings Count | shares | 876 |
| Investment Company Portfolio Turnover | 27% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 876 Portfolio Turnover 27 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 22.0 Health Care 14.9 Industrials 14.7 Information Technology 9.0 Consumer Staples 7.8 Energy 6.8 Consumer Discretionary 6.1 Real Estate 4.8 Utilities 4.8 Materials 4.5 Communication Services 4.3 Common Stocks 99.7 Short-Term Investments and Net Other Assets (Liabilities) 0.3 ASSET ALLOCATION (% of Fund's net assets) United States 99.8 Canada 0.1 Bermuda 0.1 United Kingdom 0.0 Belgium 0.0 Brazil 0.0 Puerto Rico 0.0 Japan 0.0 Luxembourg 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Berkshire Hathaway Inc Class B 3.4 JPMorgan Chase & Co 2.6 Exxon Mobil Corp 2.2 UnitedHealth Group Inc 2.0 Johnson & Johnson 1.6 Walmart Inc 1.5 Procter & Gamble Co/The 1.3 Bank of America Corp 1.2 Chevron Corp 1.1 Wells Fargo & Co 1.0 17.9 |
| Fidelity Small Cap Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Small Cap Index Fund |
| Class Name | Fidelity® Small Cap Index Fund |
| Trading Symbol | FSSNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Small Cap Index Fund for the period May 1, 2024 to October 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 Index Fund $ 0.02 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.02% |
| Net Assets | $ 26,857,343,200 |
| Holdings Count | shares | 1,983 |
| Investment Company Portfolio Turnover | 19% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 1,983 Portfolio Turnover 19 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 18.7 Health Care 17.4 Industrials 17.1 Information Technology 12.7 Consumer Discretionary 9.7 Real Estate 6.3 Energy 5.2 Materials 4.6 Utilities 2.9 Consumer Staples 2.7 Communication Services 2.6 Common Stocks 99.9 Short-Term Investments and Net Other Assets (Liabilities) 0.1 ASSET ALLOCATION (% of Fund's net assets) United States 97.0 Canada 0.6 Thailand 0.4 Puerto Rico 0.3 Argentina 0.3 Norway 0.2 Brazil 0.2 Cameroon 0.1 Monaco 0.1 Others 0.8 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) FTAI Aviation Ltd 0.6 Sprouts Farmers Market Inc 0.6 Vaxcyte Inc 0.6 Insmed Inc 0.5 Mueller Industries Inc 0.4 Fluor Corp 0.4 Applied Industrial Technologies Inc 0.4 Fabrinet 0.4 Ensign Group Inc/The 0.4 REVOLUTION Medicines Inc 0.4 4.7 |
| Fidelity Mid Cap Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Mid Cap Index Fund |
| Class Name | Fidelity® Mid Cap Index Fund |
| Trading Symbol | FSMDX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Mid Cap Index Fund for the period May 1, 2024 to October 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 Index Fund $ 0.02 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.02% |
| Net Assets | $ 36,339,516,503 |
| Holdings Count | shares | 814 |
| Investment Company Portfolio Turnover | 28% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of October 31, 2024) KEY FACTS Fund Size $ Number of Holdings 814 Portfolio Turnover 28 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Industrials 17.6 Financials 16.2 Information Technology 12.5 Consumer Discretionary 10.6 Health Care 9.7 Real Estate 7.9 Materials 5.9 Utilities 5.7 Energy 5.2 Consumer Staples 4.9 Communication Services 3.5 Common Stocks 99.7 Short-Term Investments and Net Other Assets (Liabilities) 0.3 ASSET ALLOCATION (% of Fund's net assets) United States 98.8 Brazil 0.5 Korea (South) 0.3 Canada 0.1 Bermuda 0.1 United Kingdom 0.1 Belgium 0.1 Puerto Rico 0.0 Japan 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Palantir Technologies Inc Class A 0.8 Digital Realty Trust Inc 0.6 Bank of New York Mellon Corp/The 0.6 Williams Cos Inc/The 0.5 Arthur J Gallagher & Co 0.5 AFLAC Inc 0.5 Hilton Worldwide Holdings Inc 0.5 ONEOK Inc 0.5 Simon Property Group Inc 0.5 United Rentals Inc 0.5 5.5 |
| Shareholder Report, Holdings (Details) | Oct. 31, 2024 |
| Fidelity Flex Mid Cap Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Flex Mid Cap Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Flex Mid Cap Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.20% |
| Fidelity Flex Mid Cap Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.50% |
| Fidelity Flex Mid Cap Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity Flex Mid Cap Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| Fidelity Flex Mid Cap Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.50% |
| Fidelity Flex Mid Cap Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| Fidelity Flex Mid Cap Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| Fidelity Flex Mid Cap Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| Fidelity Flex Mid Cap Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| Fidelity Flex Mid Cap Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Fidelity Flex Mid Cap Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Flex Mid Cap Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 98.70% |
| Fidelity Flex Mid Cap Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Mid Cap Index Fund | Korea, Republic of | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Flex Mid Cap Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Mid Cap Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Mid Cap Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Mid Cap Index Fund | Belgium | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Mid Cap Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Mid Cap Index Fund | Japan | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Flex Mid Cap Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Flex Mid Cap Index Fund | AAPreferredStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Flex Mid Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Series Large Cap Growth Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12% |
| Fidelity Series Large Cap Growth Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity Series Large Cap Growth Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| Fidelity Series Large Cap Growth Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| Fidelity Series Large Cap Growth Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| Fidelity Series Large Cap Growth Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity Series Large Cap Growth Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Series Large Cap Growth Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Fidelity Series Large Cap Growth Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Series Large Cap Growth Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Series Large Cap Growth Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| Fidelity Series Large Cap Growth Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 48.70% |
| Fidelity Series Large Cap Growth Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| Fidelity Series Large Cap Growth Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Series Large Cap Growth Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Series Large Cap Growth Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Series Large Cap Growth Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.10% |
| Fidelity Series Large Cap Growth Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Fidelity Series Large Cap Growth Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| Fidelity Series Large Cap Growth Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Series Large Cap Growth Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Series Large Cap Growth Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Series Large Cap Growth Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Series Large Cap Growth Index Fund | Korea, Republic of | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Series Large Cap Growth Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Large Cap Growth Index Fund | Mexico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Large Cap Growth Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.90% |
| Fidelity Series Large Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Large Cap Growth Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12% |
| Fidelity Large Cap Growth Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity Large Cap Growth Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| Fidelity Large Cap Growth Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| Fidelity Large Cap Growth Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| Fidelity Large Cap Growth Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity Large Cap Growth Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Large Cap Growth Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Fidelity Large Cap Growth Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Large Cap Growth Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Large Cap Growth Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| Fidelity Large Cap Growth Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 48.50% |
| Fidelity Large Cap Growth Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| Fidelity Large Cap Growth Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Large Cap Growth Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Large Cap Growth Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Large Cap Growth Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.10% |
| Fidelity Large Cap Growth Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Fidelity Large Cap Growth Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| Fidelity Large Cap Growth Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Large Cap Growth Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Large Cap Growth Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Large Cap Growth Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Large Cap Growth Index Fund | Korea, Republic of | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Large Cap Growth Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Growth Index Fund | Mexico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Growth Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Large Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Flex Small Cap Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Flex Small Cap Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Flex Small Cap Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Small Cap Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Flex Small Cap Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex Small Cap Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.60% |
| Fidelity Flex Small Cap Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.60% |
| Fidelity Flex Small Cap Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.20% |
| Fidelity Flex Small Cap Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| Fidelity Flex Small Cap Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17% |
| Fidelity Flex Small Cap Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Flex Small Cap Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity Flex Small Cap Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| Fidelity Flex Small Cap Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Flex Small Cap Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| Fidelity Flex Small Cap Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| Fidelity Flex Small Cap Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.10% |
| Fidelity Flex Small Cap Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Flex Small Cap Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Flex Small Cap Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Flex Small Cap Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Flex Small Cap Index Fund | Argentina | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Flex Small Cap Index Fund | Norway | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Flex Small Cap Index Fund | Cameroon | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Small Cap Index Fund | Monaco | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex Small Cap Index Fund | OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Flex Small Cap Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.30% |
| Fidelity Flex Small Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Large Cap Value Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Fidelity Large Cap Value Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Large Cap Value Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| Fidelity Large Cap Value Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity Large Cap Value Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity Large Cap Value Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity Large Cap Value Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity Large Cap Value Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Fidelity Large Cap Value Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Fidelity Large Cap Value Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Large Cap Value Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22% |
| Fidelity Large Cap Value Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9% |
| Fidelity Large Cap Value Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.90% |
| Fidelity Large Cap Value Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| Fidelity Large Cap Value Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.70% |
| Fidelity Large Cap Value Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| Fidelity Large Cap Value Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Fidelity Large Cap Value Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| Fidelity Large Cap Value Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| Fidelity Large Cap Value Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| Fidelity Large Cap Value Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| Fidelity Large Cap Value Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.80% |
| Fidelity Large Cap Value Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Large Cap Value Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Large Cap Value Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | Belgium | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | Japan | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | Luxembourg | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Large Cap Value Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Large Cap Value Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Small Cap Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.70% |
| Fidelity Small Cap Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.70% |
| Fidelity Small Cap Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| Fidelity Small Cap Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| Fidelity Small Cap Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.10% |
| Fidelity Small Cap Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Small Cap Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity Small Cap Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| Fidelity Small Cap Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Small Cap Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Fidelity Small Cap Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| Fidelity Small Cap Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97% |
| Fidelity Small Cap Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Small Cap Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Small Cap Index Fund | Argentina | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Small Cap Index Fund | Norway | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Small Cap Index Fund | Cameroon | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Index Fund | Monaco | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Small Cap Index Fund | OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Small Cap Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.90% |
| Fidelity Small Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Mid Cap Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Mid Cap Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Mid Cap Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.20% |
| Fidelity Mid Cap Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.50% |
| Fidelity Mid Cap Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity Mid Cap Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| Fidelity Mid Cap Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.60% |
| Fidelity Mid Cap Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| Fidelity Mid Cap Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| Fidelity Mid Cap Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| Fidelity Mid Cap Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Fidelity Mid Cap Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Fidelity Mid Cap Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Fidelity Mid Cap Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 98.80% |
| Fidelity Mid Cap Index Fund | Brazil | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Mid Cap Index Fund | Korea, Republic of | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Mid Cap Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Index Fund | Belgium | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Mid Cap Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Index Fund | Japan | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Mid Cap Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.70% |
| Fidelity Mid Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
