Stock-Based Compensation (Stock Option Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock Options Outstanding, Beginning	2,561
Stock options, Granted	463
Stock options, Exercised	(841)
Stock options, Forfeited	(57)
Stock Options Outstanding, Ending	2,126	2,561
Options exercisable, Shares	1,183
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding, Beginning	$ 31.16
Weighted Average Exercise Price / Share, Granted	37.90
Weighted Average Exercise Price / Share, Exercised	28.11
Weighted Average Exercise Price / Share, Forfeited	35.87
Weighted Average Exercise Price, Outstanding, Ending	33.71	$ 31.16
Options exercisable, Weighted Average Exercise Price	$ 31.01
Weighted Average Remaining Contractual Term, Outstanding	6 years 10 months 24 days	6 years 9 months 18 days
Aggregate intrinsic value of outstanding stock options	$ 34
Weighed average remaining contractual term, Options exercisable	5 years 8 months 12 days
Aggregate intrinsic value of exercisable stock options	$ 22
Vested and non-vested expected to vest as of December 31, 2016	2,060
Vested and non-vested expected to vest as of December 31, 2016	$ 33.59
Vested and non-vested expected to vest as of December 31, 2016	6 years 10 months 24 days
Aggregate intrinsic value, vested and expected to vest	$ 33