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, 2014	$ 2,101.9	$ 146.4	$ (789.5)	$ 364.8	$ 2,414.9	$ (34.7)
Beginning Balance (in shares) at Dec. 31, 2014		146.4	(13.1)
Net Income	180.9	$ 0.0	$ 0.0	0.0	180.9	0.0
Other comprehensive income (loss)	0.6	0.0	0.0	0.0	0.0	0.6
Cash dividends	(87.5)	0.0	0.0	0.0	(87.5)	0.0
Stock purchases	(263.1)	$ 0.0	$ (263.1)	0.0	0.0	0.0
Stock purchases (in shares)		0.0	(3.2)
Transfer of stock for settlement of share repurchase agreement	0.0	$ 0.0	$ 4.1	(4.1)	0.0	0.0
Transfer of stock for settlement of share repurchase agreement (in shares)		0.0	0.1
Stock based compensation expense and stock option plan transactions, including related income tax benefits	38.8	$ 0.0	$ 28.2	10.6	0.0	0.0
Stock based compensation expense and stock option plan transactions, including related income tax benefits (in shares)		0.0	0.6
Ending Balance at Jun. 30, 2015	1,971.6	$ 146.4	$ (1,020.3)	371.3	2,508.3	(34.1)
Ending Balance (in shares) at Jun. 30, 2015		146.4	(15.6)
Beginning Balance at Dec. 31, 2015	2,023.2	$ 146.4	$ (1,103.7)	376.4	2,650.0	(45.9)
Beginning Balance (in shares) at Dec. 31, 2015		146.4	(16.4)
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	(2.2)
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	0.8
Ending Balance at Jun. 30, 2016	$ 2,011.9	$ 146.4	$ (1,257.2)	$ 389.8	$ 2,782.9	$ (50.0)
Ending Balance (in shares) at Jun. 30, 2016		146.4	(17.8)