v3.25.3
Shareholder Report, Line Graph (Details) - USD ($)
12 Months Ended 60 Months Ended 96 Months Ended 108 Months Ended 132 Months Ended
Aug. 31, 2025
Aug. 31, 2025
Aug. 31, 2025
Aug. 31, 2025
Aug. 31, 2025
C000019283_0_LG_BBIndexMember_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>
C000019283_0_BBIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value $ 10,000        
C000019283_0_BBIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019283_0_BBIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019283_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019283_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019283_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000019283_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000019283_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000019283_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000019283_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000019283_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000205069_0_LG_BBIndexMember_8YRMember          
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>    
C000205069_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000205069_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,086        
C000205069_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 11,804        
C000205069_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 11,794        
C000205069_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,436        
C000205069_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,311        
C000205069_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,064        
C000205069_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,411        
C000038101_0_LG_BBIndexMember_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>
C000038101_0_BBIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000038101_0_BBIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000038101_0_BBIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000038101_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000038101_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000038101_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000038101_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000038101_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000038101_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000038101_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000038101_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000038102_0_LG_BBIndexMember_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>
C000038102_0_BBIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000038102_0_BBIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000038102_0_BBIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000038102_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000038102_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000038102_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000038102_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000038102_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000038102_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000038102_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000038102_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000038100_0_LG_BBIndexMember_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>
C000038100_0_BBIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000038100_0_BBIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000038100_0_BBIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000038100_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000038100_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000038100_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000038100_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000038100_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000038100_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000038100_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000038100_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000038098_0_LG_BBIndexMember_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>
C000038098_0_BBIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000038098_0_BBIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000038098_0_BBIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000038098_0_BBIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000038098_0_BBIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000038098_0_BBIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000038098_0_BBIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000038098_0_BBIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000038098_0_BBIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000038098_0_BBIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000038098_0_BBIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000182864_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® Total Bond K6 Fund</span>  
C000182864_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000182864_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,135        
C000182864_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 10,068        
C000182864_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 11,046        
C000182864_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 11,905        
C000182864_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 12,206        
C000182864_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,854        
C000182864_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 10,882        
C000182864_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,779        
C000182864_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>  
C000182864_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000182864_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,154        
C000182864_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 10,047        
C000182864_1_AdditionalIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 11,070        
C000182864_1_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 11,786        
C000182864_1_AdditionalIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 11,776        
C000182864_1_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,420        
C000182864_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 10,296        
C000182864_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,047        
C000019272_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® Total Bond Fund</span>
C000019272_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019272_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,694        
C000019272_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,915        
C000019272_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,855        
C000019272_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,903        
C000019272_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,810        
C000019272_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 13,116        
C000019272_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 11,618        
C000019272_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 11,661        
C000019272_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 12,655        
C000019272_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 13,135        
C000019272_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>
C000019272_1_AdditionalIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019272_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019272_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019272_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019272_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019272_1_AdditionalIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000019272_1_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000019272_1_AdditionalIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000019272_1_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000019272_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000019272_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000150510_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 Z</span>
C000150510_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000150510_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,714        
C000150510_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,946        
C000150510_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,884        
C000150510_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,946        
C000150510_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,870        
C000150510_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 13,189        
C000150510_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 11,702        
C000150510_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 11,755        
C000150510_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 12,755        
C000150510_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 13,265        
C000150510_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>
C000150510_1_AdditionalIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000150510_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000150510_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000150510_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000150510_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000150510_1_AdditionalIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000150510_1_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000150510_1_AdditionalIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,928        
C000150510_1_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000150510_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000150510_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000019276_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>
C000019276_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 9,600        
C000019276_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,244        
C000019276_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,424        
C000019276_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,324        
C000019276_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,287        
C000019276_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,113        
C000019276_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,366        
C000019276_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,929        
C000019276_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,936        
C000019276_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,821        
C000019276_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 12,246        
C000019276_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>
C000019276_1_AdditionalIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019276_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019276_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019276_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019276_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019276_1_AdditionalIndexMember_AsOf_2020Member          
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Accumulated Value 12,360        
C000019276_1_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000019276_1_AdditionalIndexMember_AsOf_2022Member          
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C000019276_1_AdditionalIndexMember_AsOf_2023Member          
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C000019276_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000019276_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
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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>
C000019277_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019277_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,699        
C000019277_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,916        
C000019277_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,839        
C000019277_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,881        
C000019277_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,781        
C000019277_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 13,080        
C000019277_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
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C000019277_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 11,625        
C000019277_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 12,598        
C000019277_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 13,083        
C000019277_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>
C000019277_1_AdditionalIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019277_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019277_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019277_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019277_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019277_1_AdditionalIndexMember_AsOf_2020Member          
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Accumulated Value 12,360        
C000019277_1_AdditionalIndexMember_AsOf_2021Member          
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Accumulated Value 12,350        
C000019277_1_AdditionalIndexMember_AsOf_2022Member          
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C000019277_1_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000019277_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000019277_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 11,949        
C000019275_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>
C000019275_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019275_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,590        
C000019275_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,695        
C000019275_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,524        
C000019275_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,417        
C000019275_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,157        
C000019275_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,316        
C000019275_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,796        
C000019275_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,720        
C000019275_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,587        
C000019275_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value 12,004        
C000019275_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>
C000019275_1_AdditionalIndexMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019275_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019275_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019275_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019275_1_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019275_1_AdditionalIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000019275_1_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,350        
C000019275_1_AdditionalIndexMember_AsOf_2022Member          
Account Value [Line Items]          
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C000019275_1_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,797        
C000019275_1_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,585        
C000019275_1_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
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C000019273_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>
C000019273_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 9,600        
C000019273_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,245        
C000019273_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,426        
C000019273_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,327        
C000019273_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,290        
C000019273_ClassMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,114        
C000019273_ClassMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 12,367        
C000019273_ClassMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,934        
C000019273_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,941        
C000019273_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 11,826        
C000019273_ClassMember_AsOf_2025Member          
Account Value [Line Items]          
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C000019273_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>
C000019273_1_AdditionalIndexMember_AsOf_2015Member          
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C000019273_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,597        
C000019273_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019273_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019273_1_AdditionalIndexMember_AsOf_2019Member          
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Accumulated Value 11,609        
C000019273_1_AdditionalIndexMember_AsOf_2020Member          
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C000019273_1_AdditionalIndexMember_AsOf_2021Member          
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C000019273_1_AdditionalIndexMember_AsOf_2022Member          
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C000019273_1_AdditionalIndexMember_AsOf_2024Member          
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C000019273_1_AdditionalIndexMember_AsOf_2025Member          
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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® Series Government Bond Index Fund</span>    
C000203458_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000203458_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 10,010        
C000203458_ClassMember_AsOf_2020Member          
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Accumulated Value 11,052        
C000203458_ClassMember_AsOf_2021Member          
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Accumulated Value 11,781        
C000203458_ClassMember_AsOf_2022Member          
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Accumulated Value 11,563        
C000203458_ClassMember_AsOf_2023Member          
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Accumulated Value 10,330        
C000203458_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 10,128        
C000203458_ClassMember_AsOf_2025Member          
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C000203458_LG_1_AdditionalIndexMember_8YRMember          
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. Government Bond Index</span>    
C000203458_1_AdditionalIndexMember_AsOf_2018Member          
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Accumulated Value 10,019        
C000203458_1_AdditionalIndexMember_AsOf_2020Member          
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C000203458_1_AdditionalIndexMember_AsOf_2021Member          
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C000203458_1_AdditionalIndexMember_AsOf_2024Member          
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C000203458_1_AdditionalIndexMember_AsOf_2025Member          
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C000203458_LG_2_AdditionalIndexMember_8YRMember          
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>    
C000203458_2_AdditionalIndexMember_AsOf_2018Member          
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Accumulated Value 10,000        
C000203458_2_AdditionalIndexMember_AsOf_2019Member          
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C000203458_2_AdditionalIndexMember_AsOf_2020Member          
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C000203458_2_AdditionalIndexMember_AsOf_2021Member          
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C000203458_2_AdditionalIndexMember_AsOf_2022Member          
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C000203458_2_AdditionalIndexMember_AsOf_2023Member          
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C000203458_2_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 10,262        
C000203458_2_AdditionalIndexMember_AsOf_2025Member          
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C000019284_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 Government Income Fund</span>
C000019284_ClassMember_AsOf_2015Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000019284_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,262        
C000019284_ClassMember_AsOf_2017Member          
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Accumulated Value 10,270        
C000019284_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,114        
C000019284_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 10,852        
C000019284_ClassMember_AsOf_2020Member          
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Accumulated Value 11,403        
C000019284_ClassMember_AsOf_2021Member          
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C000019284_ClassMember_AsOf_2023Member          
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Accumulated Value 10,286        
C000019284_ClassMember_AsOf_2024Member          
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Accumulated Value 10,898        
C000019284_ClassMember_AsOf_2025Member          
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C000019284_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 Bond Index</span>
C000019284_1_AdditionalIndexMember_AsOf_2015Member          
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C000019284_1_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
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C000019284_1_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,312        
C000019284_1_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,183        
C000019284_1_AdditionalIndexMember_AsOf_2019Member          
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C000019284_1_AdditionalIndexMember_AsOf_2020Member          
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C000019284_1_AdditionalIndexMember_AsOf_2021Member          
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C000019284_1_AdditionalIndexMember_AsOf_2022Member          
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C000019284_1_AdditionalIndexMember_AsOf_2023Member          
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C000019284_1_AdditionalIndexMember_AsOf_2024Member          
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C000019284_1_AdditionalIndexMember_AsOf_2025Member          
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C000019284_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>
C000019284_2_AdditionalIndexMember_AsOf_2015Member          
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C000019284_2_AdditionalIndexMember_AsOf_2016Member          
Account Value [Line Items]          
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C000019284_2_AdditionalIndexMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,649        
C000019284_2_AdditionalIndexMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,537        
C000019284_2_AdditionalIndexMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,609        
C000019284_2_AdditionalIndexMember_AsOf_2020Member          
Account Value [Line Items]          
Accumulated Value 12,360        
C000019284_2_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
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C000019284_2_AdditionalIndexMember_AsOf_2022Member          
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C000019284_2_AdditionalIndexMember_AsOf_2023Member          
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C000019284_2_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
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C000019284_2_AdditionalIndexMember_AsOf_2025Member          
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Line Graph and Table Measure Name         <span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;">Fidelity® Government Income Fund</span>
C000019283_ClassMember_AsOf_2015Member          
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C000019283_ClassMember_AsOf_2016Member          
Account Value [Line Items]          
Accumulated Value 10,435        
C000019283_ClassMember_AsOf_2017Member          
Account Value [Line Items]          
Accumulated Value 10,391        
C000019283_ClassMember_AsOf_2018Member          
Account Value [Line Items]          
Accumulated Value 10,227        
C000019283_ClassMember_AsOf_2019Member          
Account Value [Line Items]          
Accumulated Value 11,181        
C000019283_ClassMember_AsOf_2020Member          
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Accumulated Value 11,845        
C000019283_ClassMember_AsOf_2021Member          
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Accumulated Value 11,661        
C000019283_ClassMember_AsOf_2022Member          
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Accumulated Value 10,396        
C000019283_ClassMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 10,142        
C000019283_ClassMember_AsOf_2024Member          
Account Value [Line Items]          
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C000019283_ClassMember_AsOf_2025Member          
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Account Value [Line Items]          
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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. Government Bond Index</span>    
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C000038102_ClassMember_AsOf_2018Member          
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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. Government Bond Index</span>
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C000038102_2_AdditionalIndexMember_AsOf_2020Member          
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C000038100_ClassMember_AsOf_2018Member          
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C000038100_ClassMember_AsOf_2019Member          
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C000038100_ClassMember_AsOf_2020Member          
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C000038100_1_AdditionalIndexMember_AsOf_2020Member          
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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. Government Bond Index</span>
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Account Value [Line Items]          
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C000038100_2_AdditionalIndexMember_AsOf_2019Member          
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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>      
C000227902_2_AdditionalIndexMember_AsOf_2021Member          
Account Value [Line Items]          
Accumulated Value 10,000        
C000227902_2_AdditionalIndexMember_AsOf_2022Member          
Account Value [Line Items]          
Accumulated Value 10,126        
C000227902_2_AdditionalIndexMember_AsOf_2023Member          
Account Value [Line Items]          
Accumulated Value 8,960        
C000227902_2_AdditionalIndexMember_AsOf_2024Member          
Account Value [Line Items]          
Accumulated Value 8,853        
C000227902_2_AdditionalIndexMember_AsOf_2025Member          
Account Value [Line Items]          
Accumulated Value $ 9,499