Summary of Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Options | shares	16.0
Granted, Options | shares	1.8
Exercised, Options | shares	(1.3)
Cancelled, Options | shares	(0.1)
Ending Balance, Options | shares	16.4
Exercisable at June 30, 2017, Options | shares	10.5
Beginning Balance, Weighted-Average Exercise Price | $ / shares	$ 30.06
Granted, Weighted-Average Exercise Price | $ / shares	53.57
Exercised, Weighted-Average Exercise Price | $ / shares	21.64
Cancelled, Weighted-Average Exercise Price | $ / shares	42.59
Ending Balance, Weighted-Average Exercise Price | $ / shares	33.17
Exercisable at June 30, 2017, Weighted-Average Exercise Price | $ / shares	$ 25.35
Outstanding at June 30, 2017, Weighted-Average Remaining Contractual Term, years	6 years 1 month 6 days
Exercisable at June 30, 2017, Weighted-Average Remaining Contractual Term, years	4 years 7 months 6 days
Outstanding at June 30, 2017, Aggregate Intrinsic Value | $	$ 310.2
Exercisable at June 30, 2017, Aggregate Intrinsic Value | $	$ 278.1