Shareholder's Equity - Change in Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 1,606.3	$ 1,490.2	$ 1,573.2	$ 1,445.1	$ 1,369.5	$ 1,396.3	$ 1,573.2	$ 1,396.3
Net income	82.3	91.2	74.3	56.3	66.1	55.4	$ 247.8	177.8
Activity related to stock-based compensation	$ 13.9	20.4	12.8	16.3	19.7	10.7
Share purchased under share repurchase program (in shares)	0						761,500
Shares purchased under share repurchase program			(115.5)			(83.1)	$ (115.5)
Dividends declared	$ (11.9)		(11.8)	(11.9)	(11.4)	(10.6)
Other comprehensive income (loss), net of tax	28.3	4.5	(42.7)	(18.2)	1.2	0.8	(9.9)	(16.2)
Balance, end of period	$ 1,718.9	$ 1,606.3	$ 1,490.2	$ 1,487.6	$ 1,445.1	$ 1,369.5	1,718.9	$ 1,487.6
Dividends declared per share (in dollars per share)	$ 0.16		$ 0.16	$ 0.16	$ 0.15	$ 0.15
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			$ (0.1)				$ (0.1)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000
Balance, beginning of period	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8
Activity related to stock-based compensation	$ 0.0
Activity related to stock -based compensation (in shares)	0
Balance (in shares)	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000
Balance, end of period	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8
Capital in Excess of Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	263.1	267.6	272.7	273.4	278.5	282.0	272.7	282.0
Activity related to stock-based compensation	5.1	(4.5)	(5.1)	(4.9)	(5.1)	(3.5)
Balance, end of period	$ 268.2	$ 263.1	$ 267.6	$ 268.5	$ 273.4	$ 278.5	$ 268.2	$ 268.5
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)	1,500,000	1,700,000	1,200,000	1,600,000	1,800,000	1,200,000	1,200,000	1,200,000
Balance, beginning of period	$ (190.8)	$ (215.7)	$ (118.1)	$ (147.8)	$ (172.6)	$ (103.7)	$ (118.1)	$ (103.7)
Activity related to stock-based compensation	$ 8.8	$ 24.9	$ 17.9	$ 21.2	$ 24.8	$ 14.2
Activity related to stock -based compensation (in shares)	(100,000)	(200,000)	(300,000)	(300,000)	(200,000)	(200,000)
Share purchased under share repurchase program (in shares)			800,000			(800,000)
Shares purchased under share repurchase program			$ (115.5)			$ (83.1)
Balance (in shares)	1,400,000	1,500,000	1,700,000	1,300,000	1,600,000	1,800,000	1,400,000	1,300,000
Balance, end of period	$ (182.0)	$ (190.8)	$ (215.7)	$ (126.6)	$ (147.8)	$ (172.6)	$ (182.0)	$ (126.6)
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	1,703.0	1,611.8	1,549.4	1,452.9	1,398.2	1,353.4	1,549.4	1,353.4
Net income	82.3	91.2	74.3	56.3	66.1	55.4
Dividends declared	(11.9)		(11.8)	(11.9)	(11.4)	(10.6)
Balance, end of period	1,773.4	1,703.0	1,611.8	1,497.3	1,452.9	1,398.2	1,773.4	1,497.3
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			(0.1)				(0.1)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(187.8)	(192.3)	(149.6)	(152.2)	(153.4)	(154.2)	(149.6)	(154.2)
Other comprehensive income (loss), net of tax	28.3	4.5	(42.7)	(18.2)	1.2	0.8
Balance, end of period	$ (159.5)	$ (187.8)	$ (192.3)	$ (170.4)	$ (152.2)	$ (153.4)	$ (159.5)	$ (170.4)