Summary of Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Options | shares	16.1
Granted, Options | shares	1.9
Exercised, Options | shares	(2.5)
Cancelled, Options | shares	(0.1)
Ending Balance, Options | shares	15.4
Exercisable at September 30, 2018, Options | shares	9.5
Beginning Balance, Weighted-Average Exercise Price | $ / shares	$ 33.11
Granted, Weighted-Average Exercise Price | $ / shares	50.22
Exercised, Weighted-Average Exercise Price | $ / shares	23.40
Cancelled, Weighted-Average Exercise Price | $ / shares	48.55
Ending Balance, Weighted-Average Exercise Price | $ / shares	36.60
Exercisable at September 30, 2018, Weighted-Average Exercise Price | $ / shares	$ 29.16
Outstanding at September 30, 2018, Weighted-Average Remaining Contractual Term, years	5 years 7 months 6 days
Exercisable at September 30, 2018, Weighted-Average Remaining Contractual Term, years	4 years 1 month 6 days
Outstanding at September 30, 2018, Aggregate Intrinsic Value | $	$ 351.1
Exercisable at September 30, 2018, Aggregate Intrinsic Value | $	$ 288.0