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, 2018		$ 2,597.4	$ 78.7	$ 391.8	$ (122.1)	$ 3,351.4	$ (1,102.4)
Balance (in shares) at Dec. 31, 2018			57,900,000				20,500,000
Increase (Decrease) in Shareholders' Equity
Net income		370.2				370.2
Other comprehensive income (loss), net of tax		(22.5)			(22.5)
Dividends		(74.5)				(74.5)
Repurchases of common stock		(224.9)					$ (224.9)
Repurchases of common stock (in shares)			(1,900,000)				1,900,000
Issuances and deferrals. net for stock based compensation (1)	[1]	35.3		16.1			$ 19.2
Issuances and deferrals, net for stock based compensation (in shares)	[1]		500,000				(500,000)
Balance at the end of the period at Sep. 30, 2019		2,681.0	$ 78.7	407.9	(144.6)	3,647.1	$ (1,308.1)
Balance (in shares) at Sep. 30, 2019			56,500,000				21,900,000
Balance at the beginning of the period at Jun. 30, 2019		2,583.2	$ 78.7	400.3	(120.5)	3,537.5	$ (1,312.8)
Balance (in shares) at Jun. 30, 2019			56,400,000				22,000,000.0
Increase (Decrease) in Shareholders' Equity
Net income		137.9				137.9
Other comprehensive income (loss), net of tax		(24.1)			(24.1)
Dividends		(28.3)				(28.3)
Issuances and deferrals. net for stock based compensation (1)	[1]	12.3		7.6			$ 4.7
Issuances and deferrals, net for stock based compensation (in shares)	[1]		100,000				(100,000)
Balance at the end of the period at Sep. 30, 2019		2,681.0	$ 78.7	407.9	(144.6)	3,647.1	$ (1,308.1)
Balance (in shares) at Sep. 30, 2019			56,500,000				21,900,000
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	55,700,000				22,700,000
Increase (Decrease) in Shareholders' Equity
Net income		$ 239.5				239.5
Other comprehensive income (loss), net of tax		(7.8)			(7.8)
Dividends		(84.7)				(84.7)
Repurchases of common stock		(341.7)					$ (341.7)
Repurchases of common stock (in shares)			(2,700,000)				2,700,000
Issuances and deferrals. net for stock based compensation (1)	[1]	27.2		17.0			$ 10.2
Issuances and deferrals, net for stock based compensation (in shares)	[1]		200,000				(200,000)
Balance at the end of the period at Sep. 30, 2020		$ 2,475.3	$ 78.7	433.6	(131.9)	3,876.1	$ (1,781.2)
Balance (in shares) at Sep. 30, 2020		53,200,000	53,200,000				25,200,000
Balance at the beginning 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
Increase (Decrease) in Shareholders' Equity
Net income		102.3				102.3
Other comprehensive income (loss), net of tax		28.2			28.2
Dividends		(28.7)				(28.7)
Repurchases of common stock		(149.9)					$ (149.9)
Repurchases of common stock (in shares)			(1,200,000)				1,200,000
Issuances and deferrals. net for stock based compensation (1)	[1]	7.2		5.8			$ 1.4
Issuances and deferrals, net for stock based compensation (in shares)	[1]		0
Balance at the end of the period at Sep. 30, 2020		$ 2,475.3	$ 78.7	$ 433.6	$ (131.9)	$ 3,876.1	$ (1,781.2)
Balance (in shares) at Sep. 30, 2020		53,200,000	53,200,000				25,200,000

[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.