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, 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 (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)
Adoption of new accounting pronouncements (Note 1)	13.0	$ 0.0	$ 0.0	0.0	13.0	0.0
Net Income	615.9	0.0	0.0	0.0	615.9	0.0
Other comprehensive (loss) income	(13.1)	0.0	0.0	0.0	0.0	(13.1)
Cash dividends	(224.1)	(0.0)	(0.0)	(0.0)	(224.1)	(0.0)
Stock purchases	(250.0)	$ (0.0)	$ (250.0)	(0.0)	(0.0)	(0.0)
Stock purchases (in shares)		(0.0)	(3.6)
Stock based compensation expense and stock option plan transactions	72.3	$ 0.0	$ 57.6	14.7	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	2.2
Ending Balance at Dec. 31, 2019	2,667.8	$ 292.8	$ (2,091.2)	295.5	4,237.4	(66.7)
Ending Balance (in shares) at Dec. 31, 2019		292.8	(47.4)
Net Income	785.9	$ 0.0	$ 0.0	0.0	785.9	0.0
Other comprehensive (loss) income	(10.9)	0.0	0.0	0.0	0.0	(10.9)
Cash dividends	(237.3)	(0.0)	(0.0)	(0.0)	(237.3)	(0.0)
Stock purchases	(300.0)	$ (0.0)	$ (270.0)	(30.0)	(0.0)	(0.0)
Stock purchases (in shares)		(0.0)	(3.1)
Stock based compensation expense and stock option plan transactions	114.9	$ 0.0	$ 106.0	8.9	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	3.1
Ending Balance at Dec. 31, 2020	$ 3,020.4	$ 292.8	$ (2,255.2)	$ 274.4	$ 4,786.0	$ (77.6)
Ending Balance (in shares) at Dec. 31, 2020		292.8	(47.4)