Income Taxes - Income Tax Expense (Benefit) on Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (21)	$ 0	$ 0
Foreign	2	5	12
State	2	1	1
Total current	(17)	6	13
Deferred:
Federal	243	41	(631)
Foreign	0	2	(4)
State	12	14	(118)
Total deferred	255	57	(753)
Provision for income tax expense (benefit)	$ 238	$ 63	$ (740)