Condensed Consolidated Statement of Shareholders' Equity (Unaudited) - USD ($) $ in Millions		Total	Common Stock		Additional Paid-In Capital	Accumulated Other Comprehensive Income (loss)	Retained Earnings	Shares in Treasury
Balance at the beginning of the period at Dec. 31, 2019		$ 2,642.8	$ 78.7		$ 416.6	$ (124.1)	$ 3,721.3	$ (1,449.7)
Balance (in shares) at Dec. 31, 2019			55,700,000					22,700,000
Increase (Decrease) in Shareholders' Equity
Net income		137.2					137.2
Other comprehensive income (loss), net of tax		(36.0)				(36.0)
Dividends		(56.0)					(56.0)
Repurchases of common stock		(191.8)						$ (191.8)
Repurchases of common stock (in shares)			1,500,000					1,500,000
Issuances and deferrals. net for stock based compensation	[1]	20.0			11.2			$ 8.8
Issuances and deferrals, net for stock based compensation (in shares)	[1]		200,000					(200,000)
Balance at the end of the period at Jun. 30, 2020		2,516.2	$ 78.7		427.8	(160.1)	3,802.5	$ (1,632.7)
Balance (in shares) at Jun. 30, 2020			54,400,000					24,000,000.0
Balance at the beginning of the period at Mar. 31, 2020		2,518.5	$ 78.7		422.1	(169.6)	3,754.8	$ (1,567.5)
Balance (in shares) at Mar. 31, 2020			54,900,000					23,500,000
Increase (Decrease) in Shareholders' Equity
Net income		75.4					75.4
Other comprehensive income (loss), net of tax		9.5				9.5
Dividends		(27.7)					(27.7)
Repurchases of common stock		(66.5)						$ (66.5)
Repurchases of common stock (in shares)			500,000					500,000
Issuances and deferrals. net for stock based compensation	[1]	7.0			5.7			$ 1.3
Issuances and deferrals, net for stock based compensation (in shares)	[1]							0
Balance at the end of the period at Jun. 30, 2020		2,516.2	$ 78.7		427.8	(160.1)	3,802.5	$ (1,632.7)
Balance (in shares) at Jun. 30, 2020			54,400,000					24,000,000.0
Balance at the beginning of the period at Dec. 31, 2020		$ 2,537.7	$ 78.7		441.7	(97.0)	3,928.7	$ (1,814.4)
Balance (in shares) at Dec. 31, 2020		52,900,000	52,900,000					25,500,000
Increase (Decrease) in Shareholders' Equity
Net income		$ 151.5					151.5
Other comprehensive income (loss), net of tax		(5.8)				(5.8)
Dividends		(56.0)					(56.0)
Repurchases of common stock		(265.6)						$ (265.6)
Repurchases of common stock (in shares)			1,600,000					1,600,000
Issuances and deferrals. net for stock based compensation	[1]	56.1			18.4			$ 37.7
Issuances and deferrals, net for stock based compensation (in shares)	[1]		600,000					(600,000)
Balance at the end of the period at Jun. 30, 2021		$ 2,417.9	$ 78.7		460.1	(102.8)	4,024.2	$ (2,042.3)
Balance (in shares) at Jun. 30, 2021		51,900,000	51,900,000					26,500,000
Balance at the beginning of the period at Mar. 31, 2021		$ 2,411.8	$ 78.7		443.4	(111.1)	3,952.4	$ (1,951.6)
Balance (in shares) at Mar. 31, 2021			52,100,000					26,300,000
Increase (Decrease) in Shareholders' Equity
Net income		99.3					99.3
Other comprehensive income (loss), net of tax		8.3				8.3
Dividends		(27.5)					(27.5)
Repurchases of common stock		(115.6)						$ (115.6)
Repurchases of common stock (in shares)			600,000					600,000
Issuances and deferrals. net for stock based compensation	[1]	41.6			16.7			$ 24.9
Issuances and deferrals, net for stock based compensation (in shares)			400,000	[1]				(400,000)
Balance at the end of the period at Jun. 30, 2021		$ 2,417.9	$ 78.7		$ 460.1	$ (102.8)	$ 4,024.2	$ (2,042.3)
Balance (in shares) at Jun. 30, 2021		51,900,000	51,900,000					26,500,000

[1] Issuances and deferrals, net for stock-based compensation reflects share activity related to option exercises, restricted and performance shares vested, and net issuances and deferrals associated with deferred compensation equity.