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		164.1					164.1
Other comprehensive income (loss), net of tax		31.3				31.3
Cash dividends - $0.74 and $0.70 for the six months ended June 30, 2018 and 2017, respectively		(45.8)					(45.8)
Repurchases of common stock		(150.0)						$ (150.0)
Repurchases of common stock (in shares)			(1,500,000)					1,500,000
Issuances for stock based compensation (1)	[1]	6.0		6.3	2.8			$ (3.1)
Issuances for stock based compensation (in shares)	[1]		200,000					(200,000)
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			63,000,000.0					15,500,000
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		$ 423.3					423.3
Other comprehensive income (loss), net of tax		(10.7)				(10.7)
Cash dividends - $0.74 and $0.70 for the six months ended June 30, 2018 and 2017, respectively		(45.6)					(45.6)
Repurchases of common stock		(240.6)						$ (240.6)
Repurchases of common stock (in shares)			(2,200,000)					2,200,000
Issuances for stock based compensation (1)	[1]	11.1		12.1	(2.6)			$ 1.6
Issuances for stock based compensation (in shares)	[1]		200,000					(200,000)
Balance at the end of the period at Jun. 30, 2018		$ 2,672.3	$ 78.7	$ 365.8	$ 7.8	$ (102.9)	$ 3,211.5	$ (888.6)
Balance (in shares) at Jun. 30, 2018		59,817,890	59,800,000					18,600,000

[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.