Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Stock Options, Number of Shares
Under option, January 1, 2016 (in shares) | shares	6.4
Granted (in shares) | shares	0.6
Exercised (in shares) | shares	(1.6)
Canceled or expired (in shares) | shares	(0.1)
Under option, December 31, 2016 (in shares) | shares	5.3
Stock Options, Weighted-Average Remaining Contractual Term
Under option, January 1, 2016 (in dollars per share) | $ / shares	$ 61.44
Granted (in dollars per share) | $ / shares	91.88
Exercised (in dollars per share) | $ / shares	50.66
Canceled or expired (in dollars per share) | $ / shares	87.15
Under option, December 31, 2016 (in dollars per share) | $ / shares	$ 68.05
Stock Options
Number of shares, exercisable, December 31, 2016 (in shares) | shares	3.7
Weighted-average exercise price, exercisable, December 31, 2016 (in dollars per share) | $ / shares	$ 59.72
Weighted-average remaining contractual term, under option, December 31, 2016	5 years 10 months 25 days
Weighted-average reamaining contractual term, exercisable, December 31, 2016	4 years 10 months 25 days
Aggregate intrinsic value, under option, December 31, 2016 | $	$ 290
Aggregate intrinsic value, exercisable, December 31, 2016 | $	$ 232