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	204.4	$ 0.0	$ 0.0	0.0	204.4	0.0
Other comprehensive income (loss)	22.5	0.0	0.0	0.0	0.0	22.5
Cash dividends	(95.7)	0.0	0.0	0.0	(95.7)	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	39.2	$ 0.0	$ 32.5	6.7	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	1.3
Ending Balance at Jun. 30, 2017	1,848.3	$ 292.8	$ (1,696.0)	258.1	3,034.7	(41.3)
Ending Balance (in shares) at Jun. 30, 2017		292.8	(43.6)
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	279.5	0.0	0.0	0.0	279.5	0.0
Other comprehensive income (loss)	(12.3)	0.0	0.0	0.0	0.0	(12.3)
Cash dividends	(106.2)	0.0	0.0	0.0	(106.2)	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	44.4	$ 0.0	$ 37.2	7.2	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	1.5
Ending Balance at Jun. 30, 2018	$ 2,221.1	$ 292.8	$ (1,944.8)	$ 271.8	$ 3,650.6	$ (49.3)
Ending Balance (in shares) at Jun. 30, 2018		292.8	(47.8)