Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	28.60%	32.30%	29.10%	31.90%
Unrecognized tax benefits	$ 139		$ 139		$ 161
Accrued interest and penalties associated with unrecognized tax benefits	49		49		$ 44
Reduction of unrecognized tax benefits is reasonably possible	$ 32		$ 32