CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 0.0	$ 0.0
Balance at Beginning of Period, as Adjusted				(51.0)	8,744.0
Balance at Beginning of Period at Dec. 31, 2016		$ 30.4	$ 2,272.8	(51.0)	8,744.0	$ (2,028.2)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			4.6
Other Comprehensive Income (Loss)	$ 51.4			51.4
Net Income	229.9				229.9
Dividends to Stockholders (per common share: $0.23; $0.20)					(46.5)
Purchases of Treasury Stock	(100.0)					(100.0)
Balance at End of Period at Mar. 31, 2017	9,107.4	30.4	2,277.4	0.4	8,927.4	(2,128.2)
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption				(17.5)	14.5
Balance at Beginning of Period, as Adjusted				110.0	9,556.7
Balance at Beginning of Period at Dec. 31, 2017		30.5	2,303.3	127.5	9,542.2	(2,428.6)
Increase (Decrease) in Stockholders' Equity
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net			(0.9)
Other Comprehensive Income (Loss)	(192.4)			(192.4)
Net Income	273.5				273.5
Dividends to Stockholders (per common share: $0.23; $0.20)					(52.4)
Purchases of Treasury Stock	(100.2)					(100.2)
Balance at End of Period at Mar. 31, 2018	$ 9,499.5	$ 30.5	$ 2,302.4	$ (82.4)	$ 9,777.8	$ (2,528.8)