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, 2014	$ 2,205.0	$ 78.7	$ 247.8	$ 6.0	$ (61.8)	$ 2,134.4	$ (200.1)
Balance (in shares) at Dec. 31, 2014		64,691,059					13,723,201
Increase (Decrease) in Shareholders' Equity
Net income	319.7					319.7
Other comprehensive income (loss), net of tax	(25.3)				(25.3)
Cash dividends - $1.10, $1.30 and $1.44 per share for the years ended 2014, 2015 and 2016, respectively	(72.3)					(72.3)
Repurchases of common stock	(137.2)						$ (137.2)
Repurchases of common stock (in Shares)		(1,496,411)					1,496,411
Issuance and deferrals, net for stock based compensation (1)	57.5		45.6	2.0			$ 9.9
Issuance and deferrals, net for stock based compensation (in shares)		856,952					(836,371)
Balance at the end of the period at Dec. 31, 2015	2,347.4	$ 78.7	293.4	8.0	(87.1)	2,381.8	$ (327.4)
Balance (in shares) at Dec. 31, 2015		64,051,600					14,383,241
Increase (Decrease) in Shareholders' Equity
Net income	250.1					250.1
Other comprehensive income (loss), net of tax	(35.1)				(35.1)
Cash dividends - $1.10, $1.30 and $1.44 per share for the years ended 2014, 2015 and 2016, respectively	(84.5)					(84.5)
Repurchases of common stock	(75.7)						$ (75.7)
Repurchases of common stock (in Shares)		(782,057)					782,057
Issuance and deferrals, net for stock based compensation (1)	64.7		41.9	2.3			$ 20.5
Issuance and deferrals, net for stock based compensation (in shares)		987,639					(986,497)
Balance at the end 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	64,257,182	64,257,182					14,178,801
Increase (Decrease) in Shareholders' Equity
Net income	$ 365.5					365.5
Other comprehensive income (loss), net of tax	36.5				36.5
Cash dividends - $1.10, $1.30 and $1.44 per share for the years ended 2014, 2015 and 2016, respectively	(92.1)					(92.1)
Repurchases of common stock	(268.4)						$ (268.4)
Repurchases of common stock (in Shares)		(2,719,538)					2,719,538
Issuance and deferrals, net for stock based compensation (1)	19.9		18.4	0.1			$ 1.4
Issuance and deferrals, net for stock based compensation (in shares)		302,090					(285,146)
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	61,839,734	61,839,734					16,613,193