Income Taxes - Components of Income Tax (Benefit) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal	$ 14	$ 18	$ (7)
State	2	4	1
Foreign	54	60	37
Deferred
Federal	178	12	23
State	(3)	1	(6)
Foreign	(3)	(3)	7
Total income tax expense (benefit)	$ 242	$ 92	$ 55