| Form N-CSR Cover | 6 Months Ended |
| Aug. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Concord Street Trust |
| Entity Central Index Key | 0000819118 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Aug. 31, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Concord Street Trust |
| Entity Central Index Key | 0000819118 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| Fidelity Extended Market Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Extended Market Index Fund |
| Class Name | Fidelity® Extended Market Index Fund |
| Trading Symbol | FSMAX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Extended Market Index Fund for the period March 1, 2024 to August 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® Extended Market Index Fund $ 0.03 % |
| Expenses Paid, Amount | $ 2 |
| Expense Ratio, Percent | 0.03% |
| Net Assets | $ 41,905,374,965 |
| Holdings Count | shares | 3,569 |
| Investment Company Portfolio Turnover | 11% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 3,569 Portfolio Turnover 11 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 18.0 Industrials 17.9 Information Technology 16.7 Health Care 12.4 Consumer Discretionary 11.0 Real Estate 5.9 Materials 5.1 Energy 4.4 Communication Services 3.9 Consumer Staples 2.9 Utilities 1.6 Common Stocks 99.8 Preferred Stocks 0.0 Short-Term Investments and Net Other Assets (Liabilities) 0.2 ASSET ALLOCATION (% of Fund's net assets) United States 98.5 Canada 0.3 Puerto Rico 0.3 Bermuda 0.3 United Kingdom 0.2 Sweden 0.1 Thailand 0.1 Belgium 0.1 Switzerland 0.1 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Marvell Technology Inc 1.0 Palantir Technologies Inc Class A 1.0 CRH PLC 0.9 Workday Inc Class A 0.9 Apollo Global Management Inc 0.8 Trade Desk Inc (The) Class A 0.8 Cheniere Energy Inc 0.7 DoorDash Inc Class A 0.7 Ferguson Enterprises Inc 0.6 Snowflake Inc Class A 0.5 7.9 |
| Fidelity Total Market Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Total Market Index Fund |
| Class Name | Fidelity® Total Market Index Fund |
| Trading Symbol | FSKAX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Total Market Index Fund for the period March 1, 2024 to August 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® Total Market Index Fund $ 0.01 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.01% |
| Net Assets | $ 98,694,179,979 |
| Holdings Count | shares | 3,840 |
| Investment Company Portfolio Turnover | 3% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 3,840 Portfolio Turnover 3 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 29.4 Financials 13.9 Health Care 12.2 Consumer Discretionary 9.8 Industrials 9.6 Communication Services 8.1 Consumer Staples 5.6 Energy 3.6 Real Estate 2.8 Materials 2.6 Utilities 2.3 Common Stocks 99.9 Preferred Stocks 0.0 Short-Term Investments and Net Other Assets (Liabilities) 0.1 ASSET ALLOCATION (% of Fund's net assets) United States 99.4 Ireland 0.5 China 0.1 Puerto Rico 0.0 Canada 0.0 Bermuda 0.0 United Kingdom 0.0 Thailand 0.0 Sweden 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 6.2 Microsoft Corp 5.8 NVIDIA Corp 5.5 Amazon.com Inc 3.0 Meta Platforms Inc Class A 2.2 Alphabet Inc Class A 1.8 Berkshire Hathaway Inc Class B 1.7 Alphabet Inc Class C 1.5 Eli Lilly & Co 1.5 Broadcom Inc 1.4 30.6 |
| Fidelity Flex 500 Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity Flex® 500 Index Fund |
| Class Name | Fidelity Flex® 500 Index Fund |
| Trading Symbol | FDFIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity Flex® 500 Index Fund for the period March 1, 2024 to August 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® 500 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 | $ 5,150,835,164 |
| Holdings Count | shares | 507 |
| Investment Company Portfolio Turnover | 2% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 507 Portfolio Turnover 2 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 30.8 Financials 13.3 Health Care 12.1 Consumer Discretionary 9.6 Communication Services 8.7 Industrials 8.4 Consumer Staples 6.0 Energy 3.5 Utilities 2.4 Real Estate 2.3 Materials 2.2 Common Stocks 99.3 Short-Term Investments and Net Other Assets (Liabilities) 0.7 ASSET ALLOCATION (% of Fund's net assets) United States 99.5 Ireland 0.4 China 0.1 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 6.9 Microsoft Corp 6.5 NVIDIA Corp 6.2 Amazon.com Inc 3.4 Meta Platforms Inc Class A 2.4 Alphabet Inc Class A 2.0 Berkshire Hathaway Inc Class B 1.9 Alphabet Inc Class C 1.7 Eli Lilly & Co 1.7 Broadcom Inc 1.6 34.3 |
| Fidelity 500 Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® 500 Index Fund |
| Class Name | Fidelity® 500 Index Fund |
| Trading Symbol | FXAIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® 500 Index Fund for the period March 1, 2024 to August 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® 500 Index Fund $ 0.02 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.02% |
| Net Assets | $ 585,632,427,298 |
| Holdings Count | shares | 507 |
| Investment Company Portfolio Turnover | 3% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 507 Portfolio Turnover 3 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 31.0 Financials 13.3 Health Care 12.2 Consumer Discretionary 9.7 Communication Services 8.7 Industrials 8.4 Consumer Staples 6.0 Energy 3.5 Utilities 2.4 Real Estate 2.4 Materials 2.2 Common Stocks 99.8 Short-Term Investments and Net Other Assets (Liabilities) 0.2 ASSET ALLOCATION (% of Fund's net assets) United States 99.4 Ireland 0.5 China 0.1 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 7.0 Microsoft Corp 6.5 NVIDIA Corp 6.3 Amazon.com Inc 3.4 Meta Platforms Inc Class A 2.4 Alphabet Inc Class A 2.0 Berkshire Hathaway Inc Class B 1.9 Alphabet Inc Class C 1.7 Eli Lilly & Co 1.7 Broadcom Inc 1.6 34.5 |
| Fidelity International Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® International Index Fund |
| Class Name | Fidelity® International Index Fund |
| Trading Symbol | FSPSX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® International Index Fund for the period March 1, 2024 to August 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® International Index Fund $ 0.04 % |
| Expenses Paid, Amount | $ 2 |
| Expense Ratio, Percent | 0.04% |
| Net Assets | $ 54,665,898,945 |
| Holdings Count | shares | 748 |
| Investment Company Portfolio Turnover | 4% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 748 Portfolio Turnover 4 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Financials 20.1 Industrials 16.8 Health Care 13.8 Consumer Discretionary 10.7 Information Technology 8.6 Consumer Staples 8.6 Materials 6.1 Communication Services 4.0 Energy 3.7 Utilities 3.1 Real Estate 2.0 Common Stocks 97.0 Preferred Stocks 0.5 Short-Term Investments and Net Other Assets (Liabilities) 2.5 ASSET ALLOCATION (% of Fund's net assets) Japan 22.3 United States 11.7 United Kingdom 10.7 France 9.2 Germany 8.5 Australia 7.2 Switzerland 6.2 Netherlands 4.4 Denmark 3.7 Others 16.1 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Novo Nordisk A/S Series B 2.6 ASML Holding NV 2.0 Nestle SA 1.6 Astrazeneca PLC 1.5 Novartis AG 1.4 Roche Holding AG 1.3 SAP SE 1.3 Shell PLC 1.3 LVMH Moet Hennessy Louis Vuitton SE 1.2 Toyota Motor Corp 1.1 15.3 |
| Fidelity Series Total Market Index Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Series Total Market Index Fund |
| Class Name | Fidelity® Series Total Market Index Fund |
| Trading Symbol | FCFMX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Series Total Market Index Fund for the period March 1, 2024 to August 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 Total Market 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 | $ 73,607,561,878 |
| Holdings Count | shares | 3,964 |
| Investment Company Portfolio Turnover | 9% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 3,964 Portfolio Turnover 9 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 29.4 Financials 13.9 Health Care 12.2 Consumer Discretionary 9.8 Industrials 9.6 Communication Services 8.1 Consumer Staples 5.6 Energy 3.6 Real Estate 2.8 Materials 2.6 Utilities 2.3 Common Stocks 99.9 Preferred Stocks 0.0 Short-Term Investments and Net Other Assets (Liabilities) 0.1 ASSET ALLOCATION (% of Fund's net assets) United States 99.4 Ireland 0.5 China 0.1 Canada 0.0 Puerto Rico 0.0 Bermuda 0.0 United Kingdom 0.0 Sweden 0.0 Thailand 0.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Apple Inc 6.2 Microsoft Corp 5.8 NVIDIA Corp 5.5 Amazon.com Inc 3.0 Meta Platforms Inc Class A 2.2 Alphabet Inc Class A 1.8 Berkshire Hathaway Inc Class B 1.7 Alphabet Inc Class C 1.5 Eli Lilly & Co 1.5 Broadcom Inc 1.4 30.6 |
| Shareholder Report, Holdings (Details) | Aug. 31, 2024 |
| Fidelity Extended Market Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Extended Market Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Extended Market Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| Fidelity Extended Market Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| Fidelity Extended Market Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Extended Market Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Fidelity Extended Market Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Extended Market Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity Extended Market Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Extended Market Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Extended Market Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18% |
| Fidelity Extended Market Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.70% |
| Fidelity Extended Market Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.40% |
| Fidelity Extended Market Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| Fidelity Extended Market Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.90% |
| Fidelity Extended Market Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| Fidelity Extended Market Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| Fidelity Extended Market Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| Fidelity Extended Market Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Fidelity Extended Market Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| Fidelity Extended Market Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity Extended Market Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 98.50% |
| Fidelity Extended Market Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Extended Market Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Extended Market Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Fidelity Extended Market Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Extended Market Index Fund | Sweden | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Extended Market Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Extended Market Index Fund | Belgium | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Extended Market Index Fund | Switzerland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Extended Market Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.80% |
| Fidelity Extended Market Index Fund | AAPreferredStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Extended Market Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity Total Market Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Total Market Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| Fidelity Total Market Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| Fidelity Total Market Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Total Market Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| Fidelity Total Market Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| Fidelity Total Market Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity Total Market Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity Total Market Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity Total Market Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Total Market Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.90% |
| Fidelity Total Market Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 29.40% |
| Fidelity Total Market Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity Total Market Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Fidelity Total Market Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.60% |
| Fidelity Total Market Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Total Market Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Total Market Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.60% |
| Fidelity Total Market Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| Fidelity Total Market Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| Fidelity Total Market Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Total Market Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.40% |
| Fidelity Total Market Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | Sweden | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | Ireland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Total Market Index Fund | China | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Total Market Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.90% |
| Fidelity Total Market Index Fund | AAPreferredStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Total Market Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex 500 Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.90% |
| Fidelity Flex 500 Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| Fidelity Flex 500 Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Flex 500 Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Fidelity Flex 500 Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Fidelity Flex 500 Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity Flex 500 Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Fidelity Flex 500 Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity Flex 500 Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity Flex 500 Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity Flex 500 Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.30% |
| Fidelity Flex 500 Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.80% |
| Fidelity Flex 500 Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.10% |
| Fidelity Flex 500 Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Flex 500 Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| Fidelity Flex 500 Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| Fidelity Flex 500 Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.60% |
| Fidelity Flex 500 Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6% |
| Fidelity Flex 500 Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| Fidelity Flex 500 Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Fidelity Flex 500 Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Fidelity Flex 500 Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.50% |
| Fidelity Flex 500 Index Fund | Ireland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.40% |
| Fidelity Flex 500 Index Fund | China | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Flex 500 Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.30% |
| Fidelity Flex 500 Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Fidelity 500 Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7% |
| Fidelity 500 Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| Fidelity 500 Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| Fidelity 500 Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Fidelity 500 Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Fidelity 500 Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity 500 Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Fidelity 500 Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity 500 Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity 500 Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity 500 Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.30% |
| Fidelity 500 Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31% |
| Fidelity 500 Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity 500 Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Fidelity 500 Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| Fidelity 500 Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| Fidelity 500 Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| Fidelity 500 Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6% |
| Fidelity 500 Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| Fidelity 500 Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Fidelity 500 Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Fidelity 500 Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.40% |
| Fidelity 500 Index Fund | Ireland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity 500 Index Fund | China | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity 500 Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.80% |
| Fidelity 500 Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Fidelity International Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity International Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity International Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Fidelity International Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity International Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity International Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity International Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity International Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Fidelity International Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Fidelity International Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Fidelity International Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.10% |
| Fidelity International Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| Fidelity International Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.80% |
| Fidelity International Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity International Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.80% |
| Fidelity International Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Fidelity International Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| Fidelity International Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| Fidelity International Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Fidelity International Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity International Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity International Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.70% |
| Fidelity International Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| Fidelity International Index Fund | Switzerland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity International Index Fund | Japan | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.30% |
| Fidelity International Index Fund | France | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.20% |
| Fidelity International Index Fund | Germany | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.50% |
| Fidelity International Index Fund | Australia | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.20% |
| Fidelity International Index Fund | Netherlands | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| Fidelity International Index Fund | Denmark | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Fidelity International Index Fund | OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.10% |
| Fidelity International Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97% |
| Fidelity International Index Fund | AAPreferredStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity International Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Series Total Market Index Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Fidelity Series Total Market Index Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| Fidelity Series Total Market Index Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| Fidelity Series Total Market Index Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Series Total Market Index Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| Fidelity Series Total Market Index Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| Fidelity Series Total Market Index Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Fidelity Series Total Market Index Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity Series Total Market Index Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| Fidelity Series Total Market Index Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity Series Total Market Index Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.90% |
| Fidelity Series Total Market Index Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 29.40% |
| Fidelity Series Total Market Index Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity Series Total Market Index Fund | Real Estate Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Fidelity Series Total Market Index Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.60% |
| Fidelity Series Total Market Index Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| Fidelity Series Total Market Index Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Fidelity Series Total Market Index Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.60% |
| Fidelity Series Total Market Index Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| Fidelity Series Total Market Index Fund | Energy Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| Fidelity Series Total Market Index Fund | Utilities Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Series Total Market Index Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.40% |
| Fidelity Series Total Market Index Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | Puerto Rico | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | Bermuda | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | Sweden | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | Thailand | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | Ireland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Series Total Market Index Fund | China | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| Fidelity Series Total Market Index Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.90% |
| Fidelity Series Total Market Index Fund | AAPreferredStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0% |
| Fidelity Series Total Market Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
