Income Taxes - Components of United States and Foreign Tax (Benefit) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (22)	$ (25)	$ 0
Foreign	147	175	154
State	3	2	(1)
Current income tax expense (benefit)	128	152	153
Deferred:
Federal	408	77	74
Foreign	(8)	(328)	5
State	(15)	22	0
Deferred income tax expense (benefit)	385	(229)	79
United States and Foreign Tax (Benefit) Expense	$ 513	$ (77)	$ 232