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, 2019	$ 2,667.8	$ 292.8	$ (2,091.2)	$ 295.5	$ 4,237.4	$ (66.7)
Beginning Balance (in shares) at Dec. 31, 2019		292.8	(47.4)
Net income	229.8	$ 0.0	$ 0.0	0.0	229.8	0.0
Other comprehensive income (loss)	(32.7)	0.0	0.0	0.0	0.0	(32.7)
Cash dividends	(59.0)	(0.0)	(0.0)	(0.0)	(59.0)	(0.0)
Stock based compensation expense and stock option plan transactions	11.9	$ 0.0	$ 11.7	0.2	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	0.3
Ending Balance at Mar. 31, 2020	2,817.8	$ 292.8	$ (2,079.5)	295.7	4,408.2	(99.4)
Ending Balance (in shares) at Mar. 31, 2020		292.8	(47.1)
Beginning Balance at Dec. 31, 2019	2,667.8	$ 292.8	$ (2,091.2)	295.5	4,237.4	(66.7)
Beginning Balance (in shares) at Dec. 31, 2019		292.8	(47.4)
Net income	419.5
Other comprehensive income (loss)	(31.6)
Ending Balance at Jun. 30, 2020	2,998.8	$ 292.8	$ (2,037.3)	302.8	4,538.8	(98.3)
Ending Balance (in shares) at Jun. 30, 2020		292.8	(45.9)
Beginning Balance at Mar. 31, 2020	2,817.8	$ 292.8	$ (2,079.5)	295.7	4,408.2	(99.4)
Beginning Balance (in shares) at Mar. 31, 2020		292.8	(47.1)
Net income	189.7	$ 0.0	$ 0.0	0.0	189.7	0.0
Other comprehensive income (loss)	1.1	0.0	0.0	0.0	0.0	1.1
Cash dividends	(59.1)	(0.0)	(0.0)	(0.0)	(59.1)	(0.0)
Stock based compensation expense and stock option plan transactions	49.3	$ 0.0	$ 42.2	7.1	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	1.2
Ending Balance at Jun. 30, 2020	2,998.8	$ 292.8	$ (2,037.3)	302.8	4,538.8	(98.3)
Ending Balance (in shares) at Jun. 30, 2020		292.8	(45.9)
Beginning Balance at Dec. 31, 2020	3,020.4	$ 292.8	$ (2,255.2)	274.4	4,786.0	(77.6)
Beginning Balance (in shares) at Dec. 31, 2020		292.8	(47.4)
Net income	220.7	$ 0.0	$ 0.0	0.0	220.7	0.0
Other comprehensive income (loss)	23.0	0.0	0.0	0.0	0.0	23.0
Cash dividends	(61.9)	(0.0)	(0.0)	(0.0)	(61.9)	(0.0)
Stock purchases	(0.0)	(0.0)	$ (30.0)	30.0	(0.0)	(0.0)
Stock purchases (in shares)			(0.4)
Stock based compensation expense and stock option plan transactions	9.0	$ 0.0	$ 7.2	1.8	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	0.1
Ending Balance at Mar. 31, 2021	3,211.2	$ 292.8	$ (2,278.0)	306.2	4,944.8	(54.6)
Ending Balance (in shares) at Mar. 31, 2021		292.8	(47.7)
Beginning Balance at Dec. 31, 2020	3,020.4	$ 292.8	$ (2,255.2)	274.4	4,786.0	(77.6)
Beginning Balance (in shares) at Dec. 31, 2020		292.8	(47.4)
Net income	439.0
Other comprehensive income (loss)	11.8
Ending Balance at Jun. 30, 2021	3,377.2	$ 292.8	$ (2,271.5)	320.5	5,101.2	(65.8)
Ending Balance (in shares) at Jun. 30, 2021		292.8	(47.5)
Beginning Balance at Mar. 31, 2021	3,211.2	$ 292.8	$ (2,278.0)	306.2	4,944.8	(54.6)
Beginning Balance (in shares) at Mar. 31, 2021		292.8	(47.7)
Net income	218.3	$ 0.0	$ 0.0	0.0	218.3	0.0
Other comprehensive income (loss)	(11.2)	0.0	0.0	0.0	0.0	(11.2)
Cash dividends	(61.9)	(0.0)	(0.0)	(0.0)	(61.9)	(0.0)
Stock based compensation expense and stock option plan transactions	20.8	$ 0.0	$ 6.5	14.3	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	0.2
Ending Balance at Jun. 30, 2021	$ 3,377.2	$ 292.8	$ (2,271.5)	$ 320.5	$ 5,101.2	$ (65.8)
Ending Balance (in shares) at Jun. 30, 2021		292.8	(47.5)