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, 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	224.6	$ 0.0	$ 0.0	0.0	224.6	0.0
Other comprehensive income (loss)	(4.1)	0.0	0.0	0.0	0.0	(4.1)
Cash dividends	(91.7)	0.0	0.0	0.0	(91.7)	0.0
Stock purchases	(200.0)	$ 0.0	$ (200.0)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(4.4)
Stock based compensation expense and stock option plan transactions, including related income tax benefits	59.9	$ 0.0	$ 46.5	13.4	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	1.6
Ending Balance at Jun. 30, 2016	2,011.9	$ 292.8	$ (1,257.2)	243.4	2,782.9	(50.0)
Ending Balance (in shares) at Jun. 30, 2016		292.8	(35.6)
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)	(6.0)	0.0	(6.0)
Stock based compensation expense and stock option plan transactions, including related income tax benefits	$ 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)