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Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Income Taxes (Textuals) [Abstract]    
Effective tax rate (percent) 38.10% 39.40%
Unrecognized tax benefits from lapse of statute of limitations $ 51  
Unrecognized tax benefits that would impact effective tax rate $ 26  
FES    
Income Taxes (Textuals) [Abstract]    
Effective tax rate (percent) 33.90% 38.50%