Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	27.30%	29.50%	28.50%	30.60%
Unrecognized tax benefits	$ 138		$ 138		$ 161
Accrued interest and penalties associated with unrecognized tax benefits	53		53		$ 44
Reduction of unrecognized tax benefits is reasonably possible	$ 32		$ 32