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, 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	157.8	0.0	0.0	0.0	157.8	0.0
Other comprehensive income (loss)	3.3	0.0	0.0	0.0	0.0	3.3
Cash dividends	(53.0)	(0.0)	(0.0)	(0.0)	(53.0)	(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	19.5	$ 0.0	$ 23.7	(4.2)	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	0.9
Ending Balance at Mar. 31, 2018	2,143.3	$ 292.8	$ (1,958.3)	260.4	3,582.1	(33.7)
Ending Balance (in shares) at Mar. 31, 2018		292.8	(48.4)
Beginning Balance at Dec. 31, 2018	2,453.8	$ 292.8	$ (1,898.8)	280.8	3,832.6	(53.6)
Beginning Balance (in shares) at Dec. 31, 2018		292.8	(46.0)
Adoption of new accounting pronouncements	13.0	$ 0.0	$ 0.0	0.0	13.0	0.0
Net Income	175.7	0.0	0.0	0.0	175.7	0.0
Other comprehensive income (loss)	(5.9)	0.0	0.0	0.0	0.0	(5.9)
Cash dividends	(55.9)	(0.0)	(0.0)	(0.0)	(55.9)	(0.0)
Stock purchases	(100.0)	$ (0.0)	$ (100.0)	(0.0)	(0.0)	(0.0)
Stock purchases (in shares)		(0.0)	(1.5)
Stock based compensation expense and stock option plan transactions	18.6	$ 0.0	$ 18.1	0.5	0.0	0.0
Stock based compensation expense and stock option plan transactions (in shares)		0.0	0.7
Ending Balance at Mar. 31, 2019	$ 2,499.3	$ 292.8	$ (1,980.7)	$ 281.3	$ 3,965.4	$ (59.5)
Ending Balance (in shares) at Mar. 31, 2019		292.8	(46.8)