Income Taxes (Provision (Benefit) for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (22)	$ (6)	$ 1
State		(1)	(3)
Total	(22)	(7)	(2)
Deferred:
Federal	(71)	(22)	(1,697)
State			(304)
Foreign			(2)
Total	(71)	(22)	(2,003)
Benefit for Income Taxes	$ (93)	$ (29)	$ (2,005)