Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions		Total	Common Stock	Additional Paid-In Capital	Deferred Compensation Equity	Accumulated Other Comprehensive Income (loss).	Retained Earnings	Shares in Treasury
Balance at the beginning of the period at Dec. 31, 2016		$ 2,466.9	$ 78.7	$ 335.3	$ 10.3	$ (122.2)	$ 2,547.4	$ (382.6)
Balance (in shares) at Dec. 31, 2016			64,200,000					14,200,000
Increase (Decrease) in Shareholders' Equity
Net income		365.5					365.5
Other comprehensive income (loss), net of tax		36.5				36.5
Cash dividends - $1.44, $1.54 and $1.80 per share for the years ended 2017, 2018 and 2019, respectively		(92.1)					(92.1)
Repurchases of common stock		(268.4)						$ (268.4)
Repurchase of common stock (in shares)			(2,700,000)					2,700,000
Issuance and deferrals, net for stock based compensation (1)	[1]	19.9		18.4	0.1			$ 1.4
Issuance and deferrals, net for stock-based compensation (in shares)	[1]		300,000					(300,000)
Balance at the end of the period at Dec. 31, 2017		2,528.3	$ 78.7	353.7	10.4	(85.7)	2,820.8	$ (649.6)
Balance (in shares) at Dec. 31, 2017			61,800,000					16,600,000
Increase (Decrease) in Shareholders' Equity
Net income		611.1					611.1
Other comprehensive income (loss), net of tax		(29.9)				(29.9)
Cash dividends - $1.44, $1.54 and $1.80 per share for the years ended 2017, 2018 and 2019, respectively		(93.5)					(93.5)
Repurchases of common stock		(467.0)						$ (467.0)
Repurchase of common stock (in shares)			(4,400,000)					4,400,000
Issuance and deferrals, net for stock based compensation (1)	[1]	41.9		30.1	(2.4)			$ 14.2
Issuance and deferrals, net for stock-based compensation (in shares)	[1]		500,000					(500,000)
Balance at the end of the period at Dec. 31, 2018		$ 2,597.4	$ 78.7	383.8	8.0	(122.1)	3,351.4	$ (1,102.4)
Balance (in shares) at Dec. 31, 2018		57,957,912	57,900,000					20,500,000
Increase (Decrease) in Shareholders' Equity
Net income		$ 472.8					472.8
Other comprehensive income (loss), net of tax		(2.0)				(2.0)
Cash dividends - $1.44, $1.54 and $1.80 per share for the years ended 2017, 2018 and 2019, respectively		(102.9)					(102.9)
Repurchases of common stock		(374.9)						$ (374.9)
Repurchase of common stock (in shares)			(2,800,000)					2,800,000
Issuance and deferrals, net for stock based compensation (1)	[1]	52.4		29.9	(5.1)			$ 27.6
Issuance and deferrals, net for stock-based compensation (in shares)	[1]		600,000					(600,000)
Balance at the end of the period at Dec. 31, 2019		$ 2,642.8	$ 78.7	$ 413.7	$ 2.9	$ (124.1)	$ 3,721.3	$ (1,449.7)
Balance (in shares) at Dec. 31, 2019		55,692,544	55,700,000					22,700,000

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