Income Taxes - Summary of Tax Act Effect (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Transition tax	$ (1)	$ 93
Foreign tax credit realized	0	(31)
Write down of unremitted earnings	0	(38)
Net impact of repatriation	(1)	24
Write down of deferred tax asset due to tax rate change	(3)	37
Net impact of Tax Act	$ (4)	$ 61