Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Beginning balance (in shares) | shares	8.1
Shares, granted (in shares) | shares	0.0
Shares, exercised (in shares) | shares	(2.2)
Shares, cancelled, forfeited and expired (in shares) | shares	(0.1)
Options, Ending balance (in shares) | shares	5.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-average exercise price, Beginning balance (in dollars per share) | $ / shares	$ 45.18
Weighted-average exercise price, granted (in dollars per share) | $ / shares	90.30
Weighted-average exercise price, exercised (in dollars per share) | $ / shares	76.08
Weighted-average exercise price, cancelled, forfeited and expired (in dollars per share) | $ / shares	53.28
Weighted-average exercise price, Ending balance (in dollars per share) | $ / shares	$ 45.61
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Shares, options exercisable (in shares) | shares	5.0
Weighted-average exercise price, options exercisable (in dollars per share) | $ / shares	$ 42.10
Weighted-average remaining years of contractual term, Options outstanding at December 31, 2015	4 years 6 months
Weighted-average remaining years of contractual term, Options exercisable at December 31, 2015	4 years
Aggregate intrinsic value, options outstanding at December 31, 2015 | $	$ 308
Aggregate intrinsic value, options exercisable at December 31, 2015 | $	$ 283
Non Vested Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Beginning balance (in shares) | shares	1.6
Shares, granted (in shares) | shares	0.0
Shares, vested (in shares) | shares	(0.7)
Shares, forfeited (in shares) | shares	(0.1)
Options, Ending balance (in shares) | shares	0.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-average grant-date fair value, Beginning balance (in dollars per share) | $ / shares	$ 19.00
Weighted-average exercise price, granted (in dollars per share) | $ / shares	27.57
Weighted-average grant-date fair value, vested (in dollars per share) | $ / shares	18.24
Weighted-average exercise price, forfeited (in dollars per share) | $ / shares	17.44
Weighted-average grant-date fair value, Beginning balance (in dollars per share) | $ / shares	$ 19.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Total unrecognized compensation expense related to nonvested options | $	$ 3
Weighted-average years to be recognized over	1 year 2 months 12 days