Condensed Consolidated Statement of Shareholders' Equity (Unaudited) - 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, 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		183.7					183.7
Other comprehensive income (loss), net of tax		(4.3)				(4.3)
Cash dividends - $0.60 and $0.70 for the six months ended June 30, 2016 and 2017, respectively		(39.0)					(39.0)
Repurchases of common stock		(41.5)						$ (41.5)
Repurchases of common stock (in shares)			(459,662)					459,662
Issuances for stock based compensation (1)	[1]	43.8		25.5	2.4			$ 15.9
Issuances for stock based compensation (in shares)	[1]		808,705					(809,293)
Balance at the end of the period at Jun. 30, 2016		2,490.1	$ 78.7	318.9	10.4	(91.4)	2,526.5	$ (353.0)
Balance (in shares) at Jun. 30, 2016			64,400,643					14,033,610
Balance at the beginning of the period at Mar. 31, 2016						(76.7)
Increase (Decrease) in Shareholders' Equity
Net income		115.2
Other comprehensive income (loss), net of tax		(14.7)				(14.7)
Cash dividends - $0.60 and $0.70 for the six months ended June 30, 2016 and 2017, respectively		(19.5)
Balance at the end of the period at Jun. 30, 2016		2,490.1	$ 78.7	318.9	10.4	(91.4)	2,526.5	$ (353.0)
Balance (in shares) at Jun. 30, 2016			64,400,643					14,033,610
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		64,257,182	64,257,182					14,178,801
Increase (Decrease) in Shareholders' Equity
Net income		$ 164.1					164.1
Other comprehensive income (loss), net of tax		31.3				31.3
Cash dividends - $0.60 and $0.70 for the six months ended June 30, 2016 and 2017, respectively		(45.8)					(45.8)
Repurchases of common stock		(150.0)						$ (150.0)
Repurchases of common stock (in shares)			(1,482,114)					1,482,114
Issuances for stock based compensation (1)	[1]	6.0		6.3	2.8			$ (3.1)
Issuances for stock based compensation (in shares)	[1]		193,221					(153,606)
Balance at the end of the period at Jun. 30, 2017		$ 2,472.5	$ 78.7	341.6	13.1	(90.9)	2,665.7	$ (535.7)
Balance (in shares) at Jun. 30, 2017		62,968,289	62,968,289					15,507,309
Balance at the beginning of the period at Mar. 31, 2017						(110.5)
Increase (Decrease) in Shareholders' Equity
Net income		$ 102.3
Other comprehensive income (loss), net of tax		19.6				19.6
Cash dividends - $0.60 and $0.70 for the six months ended June 30, 2016 and 2017, respectively		(23.1)
Balance at the end of the period at Jun. 30, 2017		$ 2,472.5	$ 78.7	$ 341.6	$ 13.1	$ (90.9)	$ 2,665.7	$ (535.7)
Balance (in shares) at Jun. 30, 2017		62,968,289	62,968,289					15,507,309

[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.