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, 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	337.8	$ 0.0	$ 0.0	0.0	337.8	0.0
Other comprehensive income (loss)	28.3	0.0	0.0	0.0	0.0	28.3
Cash dividends	(143.2)	0.0	0.0	0.0	(143.2)	0.0
Stock purchases	(300.0)	$ 0.0	$ (300.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(6.0)
Stock based compensation expense and stock option plan transactions	52.3	$ 0.0	$ 43.2	9.1	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	1.8
Ending Balance at Sep. 30, 2017	1,953.1	$ 292.8	$ (1,685.3)	260.5	3,120.6	(35.5)
Ending Balance (in shares) at Sep. 30, 2017		292.8	(43.1)
Beginning Balance at Dec. 31, 2017	2,218.0	$ 292.8	$ (1,782.0)	264.6	3,479.0	(36.4)
Beginning Balance (in shares) at Dec. 31, 2017		292.8	(45.2)
Adoption of new accounting pronouncements	(2.3)	$ 0.0	$ 0.0	0.0	(1.7)	(0.6)
Net Income	425.8	0.0	0.0	0.0	425.8	0.0
Other comprehensive income (loss)	(5.9)	0.0	0.0	0.0	0.0	(5.9)
Cash dividends	(159.6)	0.0	0.0	0.0	(159.6)	0.0
Stock purchases	(200.0)	$ 0.0	$ (200.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(4.1)
Stock based compensation expense and stock option plan transactions	77.4	$ 0.0	$ 61.7	15.7	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	2.5
Ending Balance at Sep. 30, 2018	$ 2,353.4	$ 292.8	$ (1,920.3)	$ 280.3	$ 3,743.5	$ (42.9)
Ending Balance (in shares) at Sep. 30, 2018		292.8	(46.8)