v3.25.2
Shareholder Report, Holdings (Details)
Jul. 31, 2025
Fidelity SAI U.S. Value Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.20%
Fidelity SAI U.S. Value Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity SAI U.S. Value Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Fidelity SAI U.S. Value Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Fidelity SAI U.S. Value Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity SAI U.S. Value Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Fidelity SAI U.S. Value Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.10%
Fidelity SAI U.S. Value Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.80%
Fidelity SAI U.S. Value Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.50%
Fidelity SAI U.S. Value Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity SAI U.S. Value Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 24.40%
Fidelity SAI U.S. Value Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 22.70%
Fidelity SAI U.S. Value Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 15.40%
Fidelity SAI U.S. Value Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity SAI U.S. Value Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity SAI U.S. Value Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Fidelity SAI U.S. Value Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity SAI U.S. Value Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity SAI U.S. Value Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.90%
Fidelity SAI U.S. Value Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 13.40%
Fidelity SAI U.S. Value Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity SAI U.S. Value Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.60%
Fidelity SAI U.S. Value Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity SAI U.S. Value Index Fund | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI U.S. Value Index Fund | BailiwickOfJerseyMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI U.S. Value Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI U.S. Value Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI U.S. Value Index Fund | Belgium  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity SAI U.S. Value Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.40%
Fidelity SAI U.S. Value Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI U.S. Quality Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.20%
Fidelity SAI U.S. Quality Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 9.40%
Fidelity SAI U.S. Quality Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.50%
Fidelity SAI U.S. Quality Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.00%
Fidelity SAI U.S. Quality Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.20%
Fidelity SAI U.S. Quality Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
Fidelity SAI U.S. Quality Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Fidelity SAI U.S. Quality Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Fidelity SAI U.S. Quality Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity SAI U.S. Quality Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.30%
Fidelity SAI U.S. Quality Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 16.10%
Fidelity SAI U.S. Quality Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 40.60%
Fidelity SAI U.S. Quality Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.10%
Fidelity SAI U.S. Quality Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 1.70%
Fidelity SAI U.S. Quality Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.30%
Fidelity SAI U.S. Quality Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI U.S. Quality Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.20%
Fidelity SAI U.S. Quality Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity SAI U.S. Quality Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.10%
Fidelity SAI U.S. Quality Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI U.S. Quality Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 100.00%
Fidelity SAI U.S. Quality Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 97.30%
Fidelity SAI U.S. Quality Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Fidelity SAI U.S. Momentum Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.10%
Fidelity SAI U.S. Momentum Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity SAI U.S. Momentum Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity SAI U.S. Momentum Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.40%
Fidelity SAI U.S. Momentum Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.40%
Fidelity SAI U.S. Momentum Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity SAI U.S. Momentum Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.60%
Fidelity SAI U.S. Momentum Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.10%
Fidelity SAI U.S. Momentum Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.30%
Fidelity SAI U.S. Momentum Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.30%
Fidelity SAI U.S. Momentum Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 25.00%
Fidelity SAI U.S. Momentum Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 19.60%
Fidelity SAI U.S. Momentum Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity SAI U.S. Momentum Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 1.00%
Fidelity SAI U.S. Momentum Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 11.90%
Fidelity SAI U.S. Momentum Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity SAI U.S. Momentum Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.60%
Fidelity SAI U.S. Momentum Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.20%
Fidelity SAI U.S. Momentum Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.80%
Fidelity SAI U.S. Momentum Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 1.70%
Fidelity SAI U.S. Momentum Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
Fidelity SAI U.S. Momentum Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 99.40%
Fidelity SAI U.S. Momentum Index Fund | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI U.S. Momentum Index Fund | Brazil  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity SAI U.S. Momentum Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.70%
Fidelity SAI U.S. Momentum Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI U.S. Large Cap Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.20%
Fidelity SAI U.S. Large Cap Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 7.40%
Fidelity SAI U.S. Large Cap Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Fidelity SAI U.S. Large Cap Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Fidelity SAI U.S. Large Cap Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.10%
Fidelity SAI U.S. Large Cap Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Fidelity SAI U.S. Large Cap Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity SAI U.S. Large Cap Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.70%
Fidelity SAI U.S. Large Cap Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.70%
Fidelity SAI U.S. Large Cap Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Fidelity SAI U.S. Large Cap Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 13.80%
Fidelity SAI U.S. Large Cap Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 34.00%
Fidelity SAI U.S. Large Cap Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 8.80%
Fidelity SAI U.S. Large Cap Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity SAI U.S. Large Cap Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 8.60%
Fidelity SAI U.S. Large Cap Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 1.80%
Fidelity SAI U.S. Large Cap Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.40%
Fidelity SAI U.S. Large Cap Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.20%
Fidelity SAI U.S. Large Cap Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 9.80%
Fidelity SAI U.S. Large Cap Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity SAI U.S. Large Cap Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Fidelity SAI U.S. Large Cap Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 99.50%
Fidelity SAI U.S. Large Cap Index Fund | Switzerland  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI U.S. Large Cap Index Fund | BailiwickOfJerseyMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.00%
Fidelity SAI U.S. Large Cap Index Fund | Ireland  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI U.S. Large Cap Index Fund | Netherlands  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI U.S. Large Cap Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.80%
Fidelity SAI U.S. Large Cap Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity SAI Small-Mid Cap 500 Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Fidelity SAI Small-Mid Cap 500 Index Fund | MSFinancialsSectorMember  
Holdings [Line Items]  
Percent of Net Asset Value 16.70%
Fidelity SAI Small-Mid Cap 500 Index Fund | Information Technology Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.70%
Fidelity SAI Small-Mid Cap 500 Index Fund | Healthcare Sector  
Holdings [Line Items]  
Percent of Net Asset Value 8.10%
Fidelity SAI Small-Mid Cap 500 Index Fund | Real Estate Sector  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity SAI Small-Mid Cap 500 Index Fund | Industrial Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 22.20%
Fidelity SAI Small-Mid Cap 500 Index Fund | Materials Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 5.90%
Fidelity SAI Small-Mid Cap 500 Index Fund | Consumer Discretionary Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity SAI Small-Mid Cap 500 Index Fund | Consumer Staples Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Fidelity SAI Small-Mid Cap 500 Index Fund | Communications Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity SAI Small-Mid Cap 500 Index Fund | Energy Sector  
Holdings [Line Items]  
Percent of Net Asset Value 2.90%
Fidelity SAI Small-Mid Cap 500 Index Fund | Utilities Sector Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.90%
Fidelity SAI Small-Mid Cap 500 Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 98.20%
Fidelity SAI Small-Mid Cap 500 Index Fund | United Kingdom  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Fidelity SAI Small-Mid Cap 500 Index Fund | Bermuda  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI Small-Mid Cap 500 Index Fund | Puerto Rico  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI Small-Mid Cap 500 Index Fund | Brazil  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity SAI Small-Mid Cap 500 Index Fund | Finland  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI Small-Mid Cap 500 Index Fund | Canada  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI Small-Mid Cap 500 Index Fund | Guatemala  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI Small-Mid Cap 500 Index Fund | Japan  
Holdings [Line Items]  
Percent of Net Asset Value 0.10%
Fidelity SAI Small-Mid Cap 500 Index Fund | OtherMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI Small-Mid Cap 500 Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.70%
Fidelity SAI Small-Mid Cap 500 Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Fidelity SAI Real Estate Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity SAI Real Estate Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity SAI Real Estate Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.80%
Fidelity SAI Real Estate Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity SAI Real Estate Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity SAI Real Estate Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
Fidelity SAI Real Estate Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Fidelity SAI Real Estate Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity SAI Real Estate Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Fidelity SAI Real Estate Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity SAI Real Estate Index Fund | TI0Member  
Holdings [Line Items]  
Percent of Net Asset Value 34.40%
Fidelity SAI Real Estate Index Fund | TI1Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity SAI Real Estate Index Fund | TI2Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity SAI Real Estate Index Fund | TI3Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.00%
Fidelity SAI Real Estate Index Fund | TI4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.00%
Fidelity SAI Real Estate Index Fund | TI5Member  
Holdings [Line Items]  
Percent of Net Asset Value 9.50%
Fidelity SAI Real Estate Index Fund | TI6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Fidelity SAI Real Estate Index Fund | TI7Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity SAI Real Estate Index Fund | TI8Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity SAI Real Estate Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 100.00%
Fidelity SAI Real Estate Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.80%
Fidelity SAI Real Estate Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Fidelity Real Estate Index Fund | TH0Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity Real Estate Index Fund | TH1Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Fidelity Real Estate Index Fund | TH2Member  
Holdings [Line Items]  
Percent of Net Asset Value 6.80%
Fidelity Real Estate Index Fund | TH3Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity Real Estate Index Fund | TH4Member  
Holdings [Line Items]  
Percent of Net Asset Value 4.00%
Fidelity Real Estate Index Fund | TH5Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
Fidelity Real Estate Index Fund | TH6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Fidelity Real Estate Index Fund | TH7Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Fidelity Real Estate Index Fund | TH8Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Fidelity Real Estate Index Fund | TH9Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Fidelity Real Estate Index Fund | TI0Member  
Holdings [Line Items]  
Percent of Net Asset Value 34.40%
Fidelity Real Estate Index Fund | TI1Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity Real Estate Index Fund | TI2Member  
Holdings [Line Items]  
Percent of Net Asset Value 13.30%
Fidelity Real Estate Index Fund | TI3Member  
Holdings [Line Items]  
Percent of Net Asset Value 12.00%
Fidelity Real Estate Index Fund | TI4Member  
Holdings [Line Items]  
Percent of Net Asset Value 10.00%
Fidelity Real Estate Index Fund | TI5Member  
Holdings [Line Items]  
Percent of Net Asset Value 9.50%
Fidelity Real Estate Index Fund | TI6Member  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Fidelity Real Estate Index Fund | TI7Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.10%
Fidelity Real Estate Index Fund | TI8Member  
Holdings [Line Items]  
Percent of Net Asset Value 2.00%
Fidelity Real Estate Index Fund | United States  
Holdings [Line Items]  
Percent of Net Asset Value 100.00%
Fidelity Real Estate Index Fund | AACommonStocksMember  
Holdings [Line Items]  
Percent of Net Asset Value 99.80%
Fidelity Real Estate Index Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%