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		250.4					250.4
Other comprehensive income (loss), net of tax		44.9				44.9
Cash dividends - $1.14 and $1.07 for the nine months ended September 30, 2018 and 2017, respectively		(69.0)					(69.0)
Repurchases of common stock		(268.5)						$ (268.5)
Repurchases of common stock (in shares)			(2,700,000)					2,700,000
Issuances and deferrals. net for stock based compensation (1)	[1]	11.6		11.5	1.6			$ (1.5)
Issuances and deferrals, net for stock based compensation (in shares)	[1]		200,000					(200,000)
Balance at the end of the period at Sep. 30, 2017		2,436.3	$ 78.7	346.8	11.9	(77.3)	2,728.8	$ (652.6)
Balance (in shares) at Sep. 30, 2017			61,800,000					16,700,000
Increase (Decrease) in Shareholders' Equity
Adoption of accounting standards (2) | 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		$ 523.0					523.0
Other comprehensive income (loss), net of tax		(18.5)				(18.5)
Cash dividends - $1.14 and $1.07 for the nine months ended September 30, 2018 and 2017, respectively		(69.7)					(69.7)
Repurchases of common stock		(299.9)						$ (299.9)
Repurchases of common stock (in shares)			(2,700,000)					2,700,000
Issuances and deferrals. net for stock based compensation (1)	[1]	36.0		24.1	(2.1)			$ 14.0
Issuances and deferrals, net for stock based compensation (in shares)	[1]		500,000					(500,000)
Balance at the end of the period at Sep. 30, 2018		$ 2,705.7	$ 78.7	$ 377.8	$ 8.3	$ (110.7)	$ 3,287.1	$ (935.5)
Balance (in shares) at Sep. 30, 2018		59,583,235	59,600,000					18,800,000

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