Summary of Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Options | shares	16.0
Exercised, Options | shares	(1.0)
Cancelled, Options | shares	(0.1)
Ending Balance, Options | shares	14.9
Exercisable at March 31, 2017, Options | shares	8.7
Beginning Balance, Weighted-Average Exercise Price | $ / shares	$ 30.06
Exercised, Weighted-Average Exercise Price | $ / shares	22.08
Cancelled, Weighted-Average Exercise Price | $ / shares	41.97
Ending Balance, Weighted-Average Exercise Price | $ / shares	30.54
Exercisable at March 31, 2017, Weighted-Average Exercise Price | $ / shares	$ 23.01
Outstanding at March 31, 2017, Weighted-Average Remaining Contractual Term, years	5 years 9 months 18 days
Exercisable at March 31, 2017, Weighted-Average Remaining Contractual Term, years	4 years 3 months 18 days
Outstanding at March 31, 2017, Aggregate Intrinsic Value | $	$ 288.2
Exercisable at March 31, 2017, Aggregate Intrinsic Value | $	$ 233.7