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Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Income Taxes (Textuals) [Abstract]          
Effective tax rate (percent) 40.20% 10.70% 39.10% (12.20%)  
Impairment   $ 800     $ 800
Nondeductible expense from impairment of goodwill         433
Unrecognized tax benefits from lapse of statute of limitations     $ 51    
Unrecognized tax benefits that would impact effective tax rate $ 26   $ 26    
State and Local Jurisdiction          
Income Taxes (Textuals) [Abstract]          
Valuation allowance         $ 159
FES          
Income Taxes (Textuals) [Abstract]          
Effective tax rate (percent) 54.80% 24.60% 22.80% 16.60%  
Impairment   $ 23      
Nondeductible expense from impairment of goodwill   23      
FES | State and Local Jurisdiction          
Income Taxes (Textuals) [Abstract]          
Valuation allowance   $ 65   $ 65