Summary of Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Options	8.5	8.8	8.2
Granted, Options	1.1	1.1	1.7
Exercised, Options	(0.9)	(1.3)	(1.0)
Cancelled, Options	(0.1)	(0.1)	(0.1)
Ending Balance, Options	8.6	8.5	8.8
Exercisable as of December 31, 2015, Options	4.8
Beginning Balance, Weighted-Average Exercise Price	$ 45.50	$ 39.47	$ 32.81
Granted, Weighted-Average Exercise Price	83.81	69.61	61.89
Exercised, Weighted-Average Exercise Price	31.11	25.14	21.47
Cancelled, Weighted-Average Exercise Price	61.90	56.31	47.47
Ending Balance, Weighted-Average Exercise Price	51.77	$ 45.50	$ 39.47
Exercisable as of December 31, 2015, Weighted-Average Exercise Price	$ 37.06
Outstanding as of December 31, 2015, Weighted-Average Remaining Contractual Term, years	5 years 9 months 18 days
Exercisable as of December 31, 2015, Weighted-Average Remaining Contractual Term, years	4 years 1 month 6 days
Outstanding as of December 31, 2015, Aggregate Intrinsic Value	$ 284.1
Exercisable as of December 31, 2015, Aggregate Intrinsic Value	$ 230.4