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Income Taxes, Expense (Benefit) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income tax expense (benefit)      
Current federal income tax expense $ 68 $ 29 $ 97
Current state income tax expense (benefit) 10 (2) 5
Deferred federal income tax expense (benefit) (354) 1 48
Deferred state income tax expense (benefit) (11) 5 7
Total income tax expense (benefit) $ (287) $ 33 $ 157