Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	19.90%	21.60%
Unrecognized tax benefits	$ 113		$ 147
Accrued interest and penalties associated with unrecognized tax benefits	19		$ 35
Reduction of unrecognized tax benefits is reasonably possible	$ 5