v3.26.3
Shareholder Report, Line Graph (Details) - USD ($)
12 Months Ended 24 Months Ended 60 Months Ended 84 Months Ended 108 Months Ended 132 Months Ended
Aug. 31, 2026
Aug. 31, 2026
Aug. 31, 2026
Aug. 31, 2026
Aug. 31, 2026
Aug. 31, 2026
C000019124_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class M</span>
C000019124_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value $ 9,600          
C000019124_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 9,697          
C000019124_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,574          
C000019124_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,540          
C000019124_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,415          
C000019124_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,504          
C000019124_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,134          
C000019124_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,039          
C000019124_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,792          
C000019124_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,130          
C000019124_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,268          
C000019124_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019124_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019124_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019124_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019124_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019124_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019124_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019124_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019124_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019124_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019124_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019124_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000019123_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class C</span>
C000019123_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019123_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,027          
C000019123_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,814          
C000019123_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,723          
C000019123_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,522          
C000019123_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,536          
C000019123_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,085          
C000019123_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,913          
C000019123_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,575          
C000019123_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,891          
C000019123_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,041          
C000019123_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019123_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019123_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019123_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019123_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019123_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019123_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019123_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019123_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019123_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019123_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019123_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000171439_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class C</span>
C000171439_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171439_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,002          
C000171439_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,916          
C000171439_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,250          
C000171439_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,529          
C000171439_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,468          
C000171439_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,927          
C000171439_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000171439_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,601          
C000171439_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,098          
C000171439_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,361          
C000171439_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>
C000171439_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171439_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,090          
C000171439_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,106          
C000171439_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,572          
C000171439_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,960          
C000171439_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,003          
C000171439_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000171439_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,730          
C000171439_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000171439_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,930          
C000171439_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,251          
C000171439_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000171439_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171439_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000171439_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000171439_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000171439_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000171439_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000171439_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000171439_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000171439_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000171439_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000171439_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000234190_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class Z</span>      
C000234190_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234190_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,275          
C000234190_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,330          
C000234190_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,072          
C000234190_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,424          
C000234190_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234190_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234190_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234190_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234190_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234190_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000234191_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class A</span>      
C000234191_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,600          
C000234191_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 8,887          
C000234191_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 8,910          
C000234191_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,586          
C000234191_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 9,888          
C000234191_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234191_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234191_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234191_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234191_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234191_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000235214_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® SAI Sustainable Core Plus Bond Fund</span>      
C000235214_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000235214_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,587          
C000235214_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,551          
C000235214_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,249          
C000235214_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,588          
C000235214_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg MSCI U.S. Aggregate ESG Choice Bond Index</span>      
C000235214_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000235214_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,702          
C000235214_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,590          
C000235214_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,286          
C000235214_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,612          
C000235214_LG_2_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000235214_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000235214_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,696          
C000235214_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,581          
C000235214_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,280          
C000235214_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,602          
C000171440_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class I</span>
C000171440_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171440_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,097          
C000171440_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,124          
C000171440_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,558          
C000171440_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,967          
C000171440_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,005          
C000171440_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,538          
C000171440_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,778          
C000171440_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,504          
C000171440_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 12,067          
C000171440_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,377          
C000171440_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>
C000171440_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171440_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,090          
C000171440_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,106          
C000171440_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,572          
C000171440_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,960          
C000171440_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,003          
C000171440_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000171440_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,730          
C000171440_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000171440_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,930          
C000171440_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,251          
C000171440_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000171440_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171440_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000171440_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000171440_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000171440_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000171440_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000171440_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000171440_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000171440_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000171440_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000171440_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000205020_LG_ClassMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class Z</span>  
C000205020_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000205020_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,450          
C000205020_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,858          
C000205020_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,923          
C000205020_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,475          
C000205020_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,725          
C000205020_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,439          
C000205020_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 12,004          
C000205020_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,319          
C000205020_LG_1_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>  
C000205020_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000205020_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,467          
C000205020_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,851          
C000205020_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,893          
C000205020_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,460          
C000205020_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,623          
C000205020_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,288          
C000205020_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,811          
C000205020_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,129          
C000205020_LG_2_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>  
C000205020_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000205020_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,086          
C000205020_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,804          
C000205020_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,794          
C000205020_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,436          
C000205020_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,311          
C000205020_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,064          
C000205020_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,411          
C000205020_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,626          
C000221555_LG_ClassMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® SAI Low Duration Bond Fund</span>    
C000221555_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221555_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,023          
C000221555_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,985          
C000221555_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,438          
C000221555_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,064          
C000221555_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,622          
C000221555_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,067          
C000221555_LG_1_AdditionalIndexMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg US Treasury Bill: 6-9 Months Index</span>    
C000221555_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221555_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,011          
C000221555_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,972          
C000221555_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,282          
C000221555_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,835          
C000221555_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,300          
C000221555_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,699          
C000221555_LG_2_AdditionalIndexMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>    
C000221555_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221555_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 9,977          
C000221555_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 8,828          
C000221555_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 8,723          
C000221555_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,359          
C000221555_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,653          
C000221555_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 9,835          
C000201533_LG_ClassMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® SAI Total Bond Fund</span>  
C000201533_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000201533_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,067          
C000201533_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,859          
C000201533_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 12,193          
C000201533_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,847          
C000201533_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,891          
C000201533_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,836          
C000201533_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 12,328          
C000201533_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,586          
C000201533_LG_1_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>  
C000201533_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000201533_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,154          
C000201533_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,876          
C000201533_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,866          
C000201533_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,499          
C000201533_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,374          
C000201533_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,131          
C000201533_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,480          
C000201533_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,697          
C000019128_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® Short-Term Bond Fund</span>
C000019128_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019128_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,103          
C000019128_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,124          
C000019128_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,576          
C000019128_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,979          
C000019128_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,035          
C000019128_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,573          
C000019128_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,816          
C000019128_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,545          
C000019128_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 12,095          
C000019128_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,406          
C000019128_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>
C000019128_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019128_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,090          
C000019128_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,106          
C000019128_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,572          
C000019128_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,960          
C000019128_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,003          
C000019128_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000019128_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,730          
C000019128_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000019128_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,930          
C000019128_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,251          
C000019128_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019128_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019128_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019128_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019128_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019128_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019128_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019128_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019128_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019128_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019128_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019128_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000257875_LG_ClassMember_2YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name   <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® SAI Enhanced Core Bond Fund</span>        
C000257875_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000257875_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,245          
C000257875_LG_1_AdditionalIndexMember_2YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name   <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>        
C000257875_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000257875_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,261          
C000234193_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class M</span>      
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Account Value [Line Items]            
Accumulated Value 9,600          
C000234193_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 8,887          
C000234193_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 8,910          
C000234193_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,586          
C000234193_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 9,888          
C000234193_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234193_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234193_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234193_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234193_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234193_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000234194_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class I</span>      
C000234194_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234194_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,270          
C000234194_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,317          
C000234194_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000234194_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,381          
C000234194_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234194_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234194_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234194_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234194_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234194_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000171438_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class M</span>
C000171438_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 9,850          
C000171438_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 9,930          
C000171438_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,941          
C000171438_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,350          
C000171438_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,735          
C000171438_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,755          
C000171438_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,283          
C000171438_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,499          
C000171438_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,182          
C000171438_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,704          
C000171438_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,981          
C000171438_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>
C000171438_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171438_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,090          
C000171438_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,106          
C000171438_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,572          
C000171438_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,960          
C000171438_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,003          
C000171438_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000171438_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,730          
C000171438_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000171438_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,930          
C000171438_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,251          
C000171438_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000171438_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171438_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000171438_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000171438_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000171438_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000171438_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000171438_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000171438_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000171438_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000171438_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000171438_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000048836_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® Intermediate Bond Fund</span>
C000048836_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000048836_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,111          
C000048836_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,003          
C000048836_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,821          
C000048836_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,490          
C000048836_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,590          
C000048836_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,597          
C000048836_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,675          
C000048836_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,453          
C000048836_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,997          
C000048836_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,184          
C000048836_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Intermediate Government/Credit Bond Index</span>
C000048836_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000048836_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,082          
C000048836_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,980          
C000048836_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,790          
C000048836_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,432          
C000048836_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,451          
C000048836_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,512          
C000048836_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,570          
C000048836_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,321          
C000048836_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,853          
C000048836_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,066          
C000048836_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000048836_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000048836_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000048836_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000048836_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000048836_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000048836_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000048836_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000048836_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000048836_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000048836_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000048836_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000200823_LG_ClassMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity Flex® Conservative Income Bond Fund</span>  
C000200823_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000200823_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,066          
C000200823_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,348          
C000200823_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000200823_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,614          
C000200823_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,637          
C000200823_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,153          
C000200823_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,835          
C000200823_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,439          
C000200823_LG_1_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 3-6 Month Treasury Bill Index</span>  
C000200823_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000200823_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,050          
C000200823_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,302          
C000200823_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,457          
C000200823_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,466          
C000200823_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,495          
C000200823_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,945          
C000200823_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,552          
C000200823_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,084          
C000200823_LG_2_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>  
C000200823_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000200823_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,054          
C000200823_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,077          
C000200823_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,794          
C000200823_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 11,784          
C000200823_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,427          
C000200823_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,303          
C000200823_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,055          
C000200823_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000234192_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class C</span>      
C000234192_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234192_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,210          
C000234192_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,174          
C000234192_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,797          
C000234192_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,020          
C000234192_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234192_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234192_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234192_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234192_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234192_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000019121_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class A</span>
C000019121_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 9,600          
C000019121_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 9,699          
C000019121_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,578          
C000019121_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,546          
C000019121_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,422          
C000019121_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,523          
C000019121_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,151          
C000019121_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,055          
C000019121_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,809          
C000019121_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,132          
C000019121_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,285          
C000019121_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019121_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019121_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019121_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019121_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019121_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019121_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019121_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019121_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019121_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019121_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019121_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000221556_LG_ClassMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® SAI Short-Term Bond Fund</span>    
C000221556_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221556_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,054          
C000221556_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,651          
C000221556_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,863          
C000221556_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,515          
C000221556_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,039          
C000221556_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,365          
C000221556_LG_1_AdditionalIndexMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>    
C000221556_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221556_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,039          
C000221556_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 9,639          
C000221556_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,791          
C000221556_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,403          
C000221556_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,885          
C000221556_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,178          
C000221556_LG_2_AdditionalIndexMember_7YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name       <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>    
C000221556_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000221556_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 9,977          
C000221556_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 8,828          
C000221556_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 8,723          
C000221556_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,359          
C000221556_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,653          
C000221556_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 9,835          
C000234189_LG_ClassMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® Tactical Bond Fund</span>      
C000234189_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234189_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,270          
C000234189_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,317          
C000234189_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000234189_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,392          
C000234189_LG_1_AdditionalIndexMember_5YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name     <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>      
C000234189_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000234189_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 9,301          
C000234189_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 9,190          
C000234189_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 9,861          
C000234189_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 10,170          
C000205019_LG_ClassMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class Z</span>  
C000205019_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000205019_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,097          
C000205019_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 12,064          
C000205019_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 12,218          
C000205019_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,809          
C000205019_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,750          
C000205019_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,601          
C000205019_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,994          
C000205019_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,190          
C000205019_LG_1_AdditionalIndexMember_9YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>  
C000205019_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000205019_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,086          
C000205019_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,804          
C000205019_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,794          
C000205019_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,436          
C000205019_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,311          
C000205019_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,064          
C000205019_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,411          
C000205019_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,626          
C000019125_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class I</span>
C000019125_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019125_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,131          
C000019125_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,033          
C000019125_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,074          
C000019125_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 12,025          
C000019125_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 12,149          
C000019125_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,731          
C000019125_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,657          
C000019125_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,485          
C000019125_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,874          
C000019125_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,051          
C000019125_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019125_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019125_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019125_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019125_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019125_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019125_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019125_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019125_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019125_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019125_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019125_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000171437_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Class A</span>
C000171437_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 9,850          
C000171437_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 9,931          
C000171437_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,943          
C000171437_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,354          
C000171437_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,740          
C000171437_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 10,761          
C000171437_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,289          
C000171437_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,506          
C000171437_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,191          
C000171437_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,715          
C000171437_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,993          
C000171437_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. 1-3 Year Government/Credit Bond Index</span>
C000171437_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171437_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,090          
C000171437_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,106          
C000171437_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,572          
C000171437_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 10,960          
C000171437_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,003          
C000171437_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,565          
C000171437_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,730          
C000171437_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,401          
C000171437_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,930          
C000171437_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,251          
C000171437_LG_2_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000171437_2_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000171437_2_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000171437_2_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000171437_2_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000171437_2_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000171437_2_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000171437_2_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000171437_2_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000171437_2_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000171437_2_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000171437_2_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 11,489          
C000019120_LG_ClassMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® Investment Grade Bond Fund</span>
C000019120_ClassMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019120_ClassMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,136          
C000019120_ClassMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 10,042          
C000019120_ClassMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 11,091          
C000019120_ClassMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 12,047          
C000019120_ClassMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 12,177          
C000019120_ClassMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,774          
C000019120_ClassMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,690          
C000019120_ClassMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 11,527          
C000019120_ClassMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,923          
C000019120_ClassMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value 12,106          
C000019120_LG_1_AdditionalIndexMember_11YRMember            
Account Value [Line Items]            
Line Graph and Table Measure Name           <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Bloomberg U.S. Aggregate Bond Index</span>
C000019120_1_AdditionalIndexMember_AsOf_2016Member            
Account Value [Line Items]            
Accumulated Value 10,000          
C000019120_1_AdditionalIndexMember_AsOf_2017Member            
Account Value [Line Items]            
Accumulated Value 10,049          
C000019120_1_AdditionalIndexMember_AsOf_2018Member            
Account Value [Line Items]            
Accumulated Value 9,944          
C000019120_1_AdditionalIndexMember_AsOf_2019Member            
Account Value [Line Items]            
Accumulated Value 10,955          
C000019120_1_AdditionalIndexMember_AsOf_2020Member            
Account Value [Line Items]            
Accumulated Value 11,665          
C000019120_1_AdditionalIndexMember_AsOf_2021Member            
Account Value [Line Items]            
Accumulated Value 11,655          
C000019120_1_AdditionalIndexMember_AsOf_2022Member            
Account Value [Line Items]            
Accumulated Value 10,313          
C000019120_1_AdditionalIndexMember_AsOf_2023Member            
Account Value [Line Items]            
Accumulated Value 10,189          
C000019120_1_AdditionalIndexMember_AsOf_2024Member            
Account Value [Line Items]            
Accumulated Value 10,933          
C000019120_1_AdditionalIndexMember_AsOf_2025Member            
Account Value [Line Items]            
Accumulated Value 11,276          
C000019120_1_AdditionalIndexMember_AsOf_2026Member            
Account Value [Line Items]            
Accumulated Value $ 11,489