Shareholder's Equity - Change in Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Accounting Standards Update [Extensible Enumeration]							us-gaap:AccountingStandardsUpdate201613Member
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 1,829.0	$ 1,854.5	$ 1,490.2	$ 1,573.2	$ 1,854.5	$ 1,573.2
Net income	187.3	151.2	91.2	74.3	$ 338.5	165.5
Activity related to stock-based compensation	$ 21.8	2.5	20.4	12.8
Share purchased under share repurchase program (in shares)	0				479,000
Shares purchased under share repurchase program		(137.1)		(115.5)	$ (137.1)
Dividends declared	$ (12.5)	(12.5)		(11.8)
Other comprehensive income (loss), net of tax	7.0	(29.6)	4.5	(42.7)	(22.6)	(38.2)
Ending balance	$ 2,032.6	$ 1,829.0	$ 1,606.3	1,490.2	$ 2,032.6	1,606.3	$ 1,573.2
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ (0.1)		$ (0.1)
Ending balance							$ (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
Beginning balance	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8
Balance (in shares)	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000
Ending balance	$ 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]
Beginning balance	246.7	267.3	267.6	272.7	267.3	272.7
Activity related to stock-based compensation	1.3	(20.6)	(4.5)	(5.1)
Ending balance	$ 248.0	$ 246.7	$ 263.1	$ 267.6	$ 248.0	$ 263.1	$ 272.7
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)	1,500,000	1,300,000	1,700,000	1,200,000	1,300,000	1,200,000
Beginning balance	$ (281.7)	$ (167.7)	$ (215.7)	$ (118.1)	$ (167.7)	$ (118.1)
Activity related to stock -based compensation (in shares)	(200,000)	(300,000)	(200,000)	(300,000)
Activity related to stock-based compensation	$ 20.5	$ 23.1	$ 24.9	$ 17.9
Share purchased under share repurchase program (in shares)		500,000		800,000
Shares purchased under share repurchase program		$ (137.1)		$ (115.5)
Balance (in shares)	1,300,000	1,500,000	1,500,000	1,700,000	1,300,000	1,500,000	1,200,000
Ending balance	$ (261.2)	$ (281.7)	$ (190.8)	$ (215.7)	$ (261.2)	$ (190.8)	$ (118.1)
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,985.4	1,846.7	1,611.8	1,549.4	1,846.7	1,549.4
Net income	187.3	151.2	91.2	74.3
Dividends declared	(12.5)	(12.5)		(11.8)
Ending balance	2,160.2	1,985.4	1,703.0	1,611.8	2,160.2	1,703.0	1,549.4
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				(0.1)		(0.1)
Ending balance							(0.1)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(140.2)	(110.6)	(192.3)	(149.6)	(110.6)	(149.6)
Other comprehensive income (loss), net of tax	7.0	(29.6)	4.5	(42.7)
Ending balance	$ (133.2)	$ (140.2)	$ (187.8)	$ (192.3)	$ (133.2)	$ (187.8)	$ (149.6)