Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Current:
Federal	$ (19)	$ 3
State	1	6
Total	(18)	9
Deferred:
Federal	64	15
State	9	13
Total	73	28
Provision (benefit) for income taxes	$ 55	37
Valuation Allowance, Deferred Tax Asset, Decrease Amount		$ 127