CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total		Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance at Beginning of Year at Dec. 31, 2014			$ 30.2	$ 2,221.2	$ 166.4	$ 7,302.3	$ (1,198.2)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	26.0
Other Comprehensive Income (Loss)	$ (150.3)				(150.3)
Net Income	867.1					867.1
Dividends to Stockholders (per common share: $0.86; $0.77; $0.70)						(174.2)
Purchases of Treasury Stock	(426.7)	[1]					(426.7)
Balance at End of Year at Dec. 31, 2015	8,663.9		30.3	2,247.2	16.1	7,995.2	(1,624.9)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	25.6
Other Comprehensive Income (Loss)	(67.1)				(67.1)
Net Income	931.4					931.4
Dividends to Stockholders (per common share: $0.86; $0.77; $0.70)						(182.6)
Purchases of Treasury Stock	(403.3)	[1]					(403.3)
Balance at End of Year at Dec. 31, 2016	8,968.0		30.4	2,272.8	(51.0)	8,744.0	(2,028.2)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	30.5
Other Comprehensive Income (Loss)	178.5				178.5
Net Income	994.2					994.2
Dividends to Stockholders (per common share: $0.86; $0.77; $0.70)						(196.0)
Purchases of Treasury Stock	(400.4)	[1]					(400.4)
Balance at End of Year at Dec. 31, 2017	$ 9,574.9		$ 30.5	$ 2,303.3	$ 127.5	$ 9,542.2	$ (2,428.6)

[1] Includes commissions of $0.3 million, $0.2 million, and $0.3 million for the years ended December 31, 2017, 2016, and 2015, respectively.