v3.26.1
Shareholder Report, Holdings (Details)
Apr. 30, 2026
Fidelity Small Cap Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Small Cap Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.00%
Fidelity Small Cap Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Small Cap Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity Small Cap Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Small Cap Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Small Cap Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Small Cap Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Small Cap Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Small Cap Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Small Cap Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 16.60%
Fidelity Small Cap Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 16.20%
Fidelity Small Cap Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 16.30%
Fidelity Small Cap Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 5.20%
Fidelity Small Cap Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 19.20%
Fidelity Small Cap Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity Small Cap Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.00%
Fidelity Small Cap Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.70%
Fidelity Small Cap Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.50%
Fidelity Small Cap Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.30%
Fidelity Small Cap Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.80%
Fidelity Small Cap Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 96.00%
Fidelity Small Cap Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Fidelity Small Cap Index Fund | Thailand  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Small Cap Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Small Cap Index Fund | Puerto Rico  
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 | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Small Cap Index Fund | Cameroon  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
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 99.60%
Fidelity Small Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Series Large Cap Growth Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity Series Large Cap Growth Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 11.20%
Fidelity Series Large Cap Growth Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.80%
Fidelity Series Large Cap Growth Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.90%
Fidelity Series Large Cap Growth Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.90%
Fidelity Series Large Cap Growth Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Series Large Cap Growth Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Series Large Cap Growth Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Series Large Cap Growth Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Series Large Cap Growth Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity Series Large Cap Growth Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 5.60%
Fidelity Series Large Cap Growth Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 50.50%
Fidelity Series Large Cap Growth Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Series Large Cap Growth Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Series Large Cap Growth Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.60%
Fidelity Series Large Cap Growth Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Series Large Cap Growth Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.70%
Fidelity Series Large Cap Growth Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Fidelity Series Large Cap Growth Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.90%
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 0.30%
Fidelity Series Large Cap Growth Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 99.60%
Fidelity Series Large Cap Growth Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Series Large Cap Growth Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Series Large Cap Growth Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
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 | Australia  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Series Large Cap Growth Index Fund | Kazakhstan  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Series Large Cap Growth Index Fund | Germany  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Series Large Cap Growth Index Fund | GrandCaymanUKOverseasTerMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Series Large Cap Growth Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.50%
Fidelity Series Large Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Mid Cap Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.20%
Fidelity Mid Cap Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Fidelity Mid Cap Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.00%
Fidelity Mid Cap Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.00%
Fidelity Mid Cap Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Mid Cap Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Mid Cap Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Mid Cap Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity Mid Cap Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Mid Cap Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Mid Cap Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.70%
Fidelity Mid Cap Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 14.80%
Fidelity Mid Cap Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%
Fidelity Mid Cap Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.80%
Fidelity Mid Cap Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 19.30%
Fidelity Mid Cap Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.20%
Fidelity Mid Cap Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.50%
Fidelity Mid Cap Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Mid Cap Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Mid Cap Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Mid Cap Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Mid Cap Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.40%
Fidelity Mid Cap Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Mid Cap Index Fund | Switzerland  
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 0.10%
Fidelity Mid Cap Index Fund | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Mid Cap Index Fund | Brazil  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Mid Cap Index Fund | Korea, Republic of  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Mid Cap Index Fund | Australia  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Mid Cap Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Mid Cap Index Fund | Guatemala  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Mid Cap Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.80%
Fidelity Mid Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Large Cap Value Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.80%
Fidelity Large Cap Value Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Fidelity Large Cap Value Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.50%
Fidelity Large Cap Value Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.20%
Fidelity Large Cap Value Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Large Cap Value Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Large Cap Value Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.80%
Fidelity Large Cap Value Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.80%
Fidelity Large Cap Value Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Fidelity Large Cap Value Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
Fidelity Large Cap Value Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 19.40%
Fidelity Large Cap Value Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 14.20%
Fidelity Large Cap Value Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 10.80%
Fidelity Large Cap Value Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 3.90%
Fidelity Large Cap Value Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.50%
Fidelity Large Cap Value Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity Large Cap Value Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.00%
Fidelity Large Cap Value Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.20%
Fidelity Large Cap Value Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.40%
Fidelity Large Cap Value Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity Large Cap Value Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.40%
Fidelity Large Cap Value Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 99.50%
Fidelity Large Cap Value Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Large Cap Value Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Value Index Fund | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Large Cap Value Index Fund | Brazil  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Value Index Fund | Australia  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Large Cap Value Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Value Index Fund | Guatemala  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Value Index Fund | Mexico  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Value Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.80%
Fidelity Large Cap Value Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Large Cap Growth Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity Large Cap Growth Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 11.20%
Fidelity Large Cap Growth Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.80%
Fidelity Large Cap Growth Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.90%
Fidelity Large Cap Growth Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.90%
Fidelity Large Cap Growth Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.30%
Fidelity Large Cap Growth Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Fidelity Large Cap Growth Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Large Cap Growth Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Large Cap Growth Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity Large Cap Growth Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 5.60%
Fidelity Large Cap Growth Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 50.50%
Fidelity Large Cap Growth Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity Large Cap Growth Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Large Cap Growth Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.60%
Fidelity Large Cap Growth Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Large Cap Growth Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.70%
Fidelity Large Cap Growth Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Fidelity Large Cap Growth Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.90%
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 0.30%
Fidelity Large Cap Growth Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 99.60%
Fidelity Large Cap Growth Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Large Cap Growth Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Growth Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
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 | Australia  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Growth Index Fund | Kazakhstan  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Growth Index Fund | Germany  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Growth Index Fund | GrandCaymanUKOverseasTerMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Large Cap Growth Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.50%
Fidelity Large Cap Growth Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
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 0.40%
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 0.30%
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 14.90%
Fidelity Flex Small Cap Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 16.50%
Fidelity Flex Small Cap Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Fidelity Flex Small Cap Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 16.00%
Fidelity Flex Small Cap Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Flex Small Cap Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.90%
Fidelity Flex Small Cap Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity Flex Small Cap Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity Flex Small Cap Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.20%
Fidelity Flex Small Cap Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.20%
Fidelity Flex Small Cap Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 97.90%
Fidelity Flex Small Cap Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Small Cap Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Index Fund | Norway  
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 0.30%
Fidelity Flex Small Cap Index Fund | Japan  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Index Fund | Singapore  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Index Fund | BahamasNassauMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
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 Flex Mid Cap Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
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 0.60%
Fidelity Flex Mid Cap Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
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 14.20%
Fidelity Flex Mid Cap Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 11.10%
Fidelity Flex Mid Cap Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.70%
Fidelity Flex Mid Cap Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 21.00%
Fidelity Flex Mid Cap Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.20%
Fidelity Flex Mid Cap Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 11.50%
Fidelity Flex Mid Cap Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
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 3.60%
Fidelity Flex Mid Cap Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity Flex Mid Cap Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.50%
Fidelity Flex Mid Cap Index Fund | Thailand  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Flex Mid Cap Index Fund | Switzerland  
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 0.20%
Fidelity Flex Mid Cap Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Flex Mid Cap Index Fund | Sweden  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Mid Cap Index Fund | Belgium  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Mid Cap Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.60%
Fidelity Flex Mid Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Mid Cap Index Fund | AAPreferredStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Flex Mid Cap Focused Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.90%
Fidelity Flex Mid Cap Focused Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity Flex Mid Cap Focused Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity Flex Mid Cap Focused Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity Flex Mid Cap Focused Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity Flex Mid Cap Focused Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Flex Mid Cap Focused Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Flex Mid Cap Focused Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Flex Mid Cap Focused Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Mid Cap Focused Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Mid Cap Focused Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 16.20%
Fidelity Flex Mid Cap Focused Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 14.40%
Fidelity Flex Mid Cap Focused Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 11.30%
Fidelity Flex Mid Cap Focused Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
Fidelity Flex Mid Cap Focused Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 20.80%
Fidelity Flex Mid Cap Focused Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity Flex Mid Cap Focused Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 11.50%
Fidelity Flex Mid Cap Focused Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Fidelity Flex Mid Cap Focused Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Fidelity Flex Mid Cap Focused Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 3.60%
Fidelity Flex Mid Cap Focused Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.90%
Fidelity Flex Mid Cap Focused Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.60%
Fidelity Flex Mid Cap Focused Index Fund | Thailand  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Mid Cap Focused Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Mid Cap Focused Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Mid Cap Focused Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Mid Cap Focused Index Fund | Sweden  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Mid Cap Focused Index Fund | Belgium  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity Flex Mid Cap Focused Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.70%
Fidelity Flex Mid Cap Focused Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Flex Small Cap Focused Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity Flex Small Cap Focused Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Focused Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Focused Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Focused Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity Flex Small Cap Focused Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Small Cap Focused Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Small Cap Focused Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity Flex Small Cap Focused Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Flex Small Cap Focused Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity Flex Small Cap Focused Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 18.70%
Fidelity Flex Small Cap Focused Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 14.80%
Fidelity Flex Small Cap Focused Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 16.70%
Fidelity Flex Small Cap Focused Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 5.40%
Fidelity Flex Small Cap Focused Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 16.20%
Fidelity Flex Small Cap Focused Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Fidelity Flex Small Cap Focused Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.80%
Fidelity Flex Small Cap Focused Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity Flex Small Cap Focused Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity Flex Small Cap Focused Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.10%
Fidelity Flex Small Cap Focused Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Flex Small Cap Focused Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.40%
Fidelity Flex Small Cap Focused Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Norway  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | OtherMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Japan  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Singapore  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Flex Small Cap Focused Index Fund | Ghana  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Small Cap Focused Index Fund | Israel  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity Flex Small Cap Focused Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.70%
Fidelity Flex Small Cap Focused Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%