CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 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	459.0	$ 0.0	$ 0.0	0.0	459.0	0.0
Other comprehensive (loss) income	(17.9)	0.0	0.0	0.0	0.0	(17.9)
Cash dividends	(183.0)	0.0	0.0	0.0	(183.0)	0.0
Stock purchases	(400.0)	$ 0.0	$ (400.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(9.0)
Stock based compensation expense and stock option plan transactions	96.6	$ 0.0	$ 75.2	21.4	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	2.9
Ending Balance at Dec. 31, 2016	1,977.9	$ 292.8	$ (1,428.5)	251.4	2,926.0	(63.8)
Ending Balance (in shares) at Dec. 31, 2016		292.8	(38.9)
Net Income	743.4	$ 0.0	$ 0.0	0.0	743.4	0.0
Other comprehensive (loss) income	27.4	0.0	0.0	0.0	0.0	27.4
Cash dividends	(190.4)	0.0	0.0	0.0	(190.4)	0.0
Stock purchases	(400.0)	$ 0.0	$ (400.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(8.2)
Stock based compensation expense and stock option plan transactions	59.7	$ 0.0	$ 46.5	13.2	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	1.9
Ending Balance at Dec. 31, 2017	2,218.0	$ 292.8	$ (1,782.0)	264.6	3,479.0	(36.4)
Ending Balance (in shares) at Dec. 31, 2017		292.8	(45.2)
Adoption of new accounting pronouncements (Note 1)	(2.3)	$ 0.0	$ 0.0	0.0	(1.7)	(0.6)
Net Income	568.6	0.0	0.0	0.0	568.6	0.0
Other comprehensive (loss) income	(16.6)	0.0	0.0	0.0	0.0	(16.6)
Cash dividends	(213.3)	0.0	0.0	0.0	(213.3)	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	99.4	$ 0.0	$ 83.2	16.2	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	3.3
Ending Balance at Dec. 31, 2018	$ 2,453.8	$ 292.8	$ (1,898.8)	$ 280.8	$ 3,832.6	$ (53.6)
Ending Balance (in shares) at Dec. 31, 2018		292.8	(46.0)