Net Income Per Share , Calculation of Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Line Items]
Net income	$ 123.4	$ 80.2	$ 341.8	$ 213.5
Basic shares:
Weighted-average common shares outstanding-basic (in shares)	162.1	171.3	164.8	170.9
Diluted shares:
Weighted-average common shares outstanding-basic (in shares)	162.1	171.3	164.8	170.9
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income per share (in shares)	165.6	174.8	168.4	174.9
Net income per share:
Basic (in dollars per share)	$ 0.76	$ 0.47	$ 2.07	$ 1.25
Diluted (in dollars per share)	$ 0.75	$ 0.46	$ 2.03	$ 1.22
Restricted Stock Units (RSUs) [Member]
Effect of potentially dilutive securities:
RSUs and stock options (in shares)	2.3	2.4	2.4	2.9
Stock Options [Member]
Effect of potentially dilutive securities:
RSUs and stock options (in shares)	1.2	1.1	1.2	1.1