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