CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2015	$ 2,023.2	$ 292.8	$ (1,103.7)	$ 230.0	$ 2,650.0	$ (45.9)
Beginning Balance (in shares) at Dec. 31, 2015		292.8	(32.8)
Net Income	113.0	$ 0.0	$ 0.0	0.0	113.0	0.0
Other comprehensive income (loss)	3.2	0.0	0.0	0.0	0.0	3.2
Cash dividends	(46.1)	0.0	0.0	0.0	(46.1)	0.0
Stock purchases	(200.0)	$ 0.0	$ (200.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(4.4)
Stock based compensation expense and stock option plan transactions, including related income tax benefits	27.0	$ 0.0	$ 22.4	4.6	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	0.6
Ending Balance at Mar. 31, 2016	1,920.3	$ 292.8	$ (1,281.3)	234.6	2,716.9	(42.7)
Ending Balance (in shares) at Mar. 31, 2016		292.8	(36.6)
Beginning Balance at Dec. 31, 2016	1,977.9	$ 292.8	$ (1,428.5)	251.4	2,926.0	(63.8)
Beginning Balance (in shares) at Dec. 31, 2016		292.8	(38.9)
Net Income	131.5	$ 0.0	$ 0.0	0.0	131.5	0.0
Other comprehensive income (loss)	7.3	0.0	0.0	0.0	0.0	7.3
Cash dividends	(48.4)	0.0	0.0	0.0	(48.4)	0.0
Stock purchases	$ (157.1)	$ 0.0	$ (157.1)	0.0	0.0	0.0
Stock purchases (in shares)	(3.1)	0.0	(3.1)
Stock based compensation expense and stock option plan transactions, including related income tax benefits	$ 24.5	$ 0.0	$ 26.5	(2.0)	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	1.0
Ending Balance at Mar. 31, 2017	$ 1,935.7	$ 292.8	$ (1,559.1)	$ 249.4	$ 3,009.1	$ (56.5)
Ending Balance (in shares) at Mar. 31, 2017		292.8	(41.0)