Income Taxes - Summary of Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense:
Federal	$ 186	$ 12	$ (41)
State	42	6	6
Foreign	167	130	65
Current income tax expense	395	148	30
Deferred income tax (benefit) expense:
Federal	(273)	(94)	(5)
State	(25)	(1)	(3)
Foreign	(10)	(8)	(6)
Deferred income tax (benefit) expense:	(308)	(103)	(14)
Income tax expense	$ 87	$ 45	$ 16