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, 2016		$ 2,466.9	$ 78.7	$ 335.3	$ 10.3	$ (122.2)	$ 2,547.4	$ (382.6)
Balance (in shares) at Dec. 31, 2016			64,300,000					14,200,000
Increase (Decrease) in Shareholders' Equity
Net income		61.8					61.8
Other comprehensive income (loss), net of tax		11.7				11.7
Cash dividends - $0.37 and $0.35 for the three months ended March 31, 2018 and 2017, respectively		(22.7)					(22.7)
Issuances for stock based compensation (1)	[1]	0.5		3.2	1.6			$ (4.3)
Issuances for stock based compensation (in shares)	[1]		100,000					(100,000)
Balance at the end of the period at Mar. 31, 2017		2,518.2	$ 78.7	338.5	11.9	(110.5)	2,586.5	$ (386.9)
Balance (in shares) at Mar. 31, 2017			64,400,000					14,100,000
Increase (Decrease) in Shareholders' Equity
Adoption of accounting standards | Adjustments for New Accounting Pronouncement	[2]	6.5				(6.5)	13.0
Balance at the beginning 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	61,800,000					16,600,000
Increase (Decrease) in Shareholders' Equity
Net income		$ 309.6					309.6
Other comprehensive income (loss), net of tax		23.3				23.3
Cash dividends - $0.37 and $0.35 for the three months ended March 31, 2018 and 2017, respectively		(23.1)					(23.1)
Repurchases of common stock		(129.3)						$ (129.3)
Repurchases of common stock (in shares)			(1,200,000)					1,200,000
Issuances for stock based compensation (1)	[1]	5.5		3.9	0.7			$ 0.9
Issuances for stock based compensation (in shares)	[1]		100,000					(100,000)
Balance at the end of the period at Mar. 31, 2018		$ 2,720.8	$ 78.7	$ 357.6	$ 11.1	$ (68.9)	$ 3,120.3	$ (778.0)
Balance (in shares) at Mar. 31, 2018		60,759,416	60,700,000					17,700,000

[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.

[2] Refer to Note 2 for further information regarding new accounting standards adopted.