Income Taxes - U.S. Tax Reform Legislation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Line Items]
Tax impact of global intangible low-taxed income ("GILTI") provisions of U.S. tax reform
Adjustments to provisional tax expense (benefit) first recognized in 2017 as a result of U.S. tax reform legislation	$ (7)	$ 0	$ (7)	$ 0