Change in Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,573.2	$ 1,396.3
Cumulative effect of new accounting principle in period of adoption	(0.1)
Net income	74.3	55.4
Activity related to stock-based compensation	$ 12.8	10.7
Share purchased under share repurchase program (in shares)	761,500
Shares purchased under share repurchase program	$ (115.5)	(83.1)
Dividends declared	(11.8)	(10.6)
Other comprehensive income, net of tax	(42.7)	0.8
Balance	1,490.2	1,369.5
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 18.8	$ 18.8
Balance (in shares)	75,300,000	75,300,000
Shares issued under stock plans (in shares)	0	0
Activity related to stock-based compensation	$ 0.0	$ 0.0
Balance	$ 18.8	$ 18.8
Balance (in shares)	75,300,000	75,300,000
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 272.7	$ 282.0
Activity related to stock-based compensation	(5.1)	(3.5)
Balance	267.6	278.5
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (118.1)	$ (103.7)
Balance (in shares)	1,200,000	1,200,000
Shares issued under stock plans (in shares)	(300,000)	(200,000)
Activity related to stock-based compensation	$ 17.9	$ 14.2
Share purchased under share repurchase program (in shares)	800,000	800,000
Shares purchased under share repurchase program	$ (115.5)	$ (83.1)
Balance	$ (215.7)	$ (172.6)
Balance (in shares)	1,700,000	1,800,000
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,549.4	$ 1,353.4
Cumulative effect of new accounting principle in period of adoption	(0.1)
Net income	74.3	55.4
Dividends declared	11.8	(10.6)
Balance	1,611.8	1,398.2
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(149.6)	(154.2)
Other comprehensive income, net of tax	(42.7)	0.8
Balance	$ (192.3)	$ (153.4)