CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - 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, 2012	$ 1,759.6	$ 2.1	$ (562.4)	$ 1,535.0	$ 838.3	$ (53.4)
Beginning balance (in shares) at Dec. 31, 2012		208.6	(32.5)
Comprehensive income	198.7				203.9	(5.2)
Proceeds from issuance of common stock, net	744.9	$ 0.2		744.7
Proceeds from issuance of common stock, net, shares		24.7
Restricted stock awards, stock options exercised and stock plan purchases	17.3		$ 48.0	(30.7)
Restricted stock awards, stock options exercised and stock plan purchases (in shares)			3.0
Restricted stock awards cancelled and shares tendered	(47.8)		$ (52.7)	4.9
Restricted stock awards cancelled and shares tendered (in shares)			(2.0)
Stock-based compensation	95.8			95.8
Shares repurchased	(250.0)		$ (250.0)
Shares repurchased (in shares)			(8.4)
Equity component of convertible notes, net of tax and other	31.2			31.2
Ending balance at Dec. 31, 2013	2,549.7	$ 2.3	$ (817.1)	2,380.9	1,042.2	(58.6)
Ending balance (in shares) at Dec. 31, 2013		233.3	(39.9)
Comprehensive income	120.4				242.5	(122.1)
Restricted stock awards, stock options exercised and stock plan purchases	6.7		$ 94.7	(88.0)
Restricted stock awards, stock options exercised and stock plan purchases (in shares)			5.9
Restricted stock awards cancelled and shares tendered	(41.8)		$ (82.3)	40.5
Restricted stock awards cancelled and shares tendered (in shares)			(2.1)
Stock-based compensation	49.7			49.7
Shares repurchased	(207.8)		$ (207.8)
Shares repurchased (in shares)			(5.2)
Equity component of convertible notes, net of tax and other	132.4			132.4
Ending balance at Dec. 31, 2014	2,609.3	$ 2.3	$ (1,012.5)	2,515.5	1,284.7	(180.7)
Ending balance (in shares) at Dec. 31, 2014		233.3	(41.3)
Comprehensive income	(34.9)				146.5	(181.4)
Proceeds from issuance of common stock, net	1,447.8	$ 0.3		1,447.5
Proceeds from issuance of common stock, net, shares		28.4
Restricted stock awards, stock options exercised and stock plan purchases	7.2		$ 42.3	(35.1)
Restricted stock awards, stock options exercised and stock plan purchases (in shares)			2.6
Restricted stock awards cancelled and shares tendered	(18.2)		$ (53.2)	35.0
Restricted stock awards cancelled and shares tendered (in shares)			(1.3)
Stock-based compensation	131.3			131.3
Shares repurchased	(90.2)		$ (90.2)
Shares repurchased (in shares)			(1.9)
Ending balance at Dec. 31, 2015	$ 4,052.3	$ 2.6	$ (1,113.6)	$ 4,094.2	$ 1,431.2	$ (362.1)
Ending balance (in shares) at Dec. 31, 2015		261.7	(41.9)