CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Cash and Cash Equivalents [Abstract]
Cash	$ 14.7		$ 62.1
Money market funds	33.5		40.1
Cash and cash equivalents	48.2	60.2	102.2	89.5
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	1,081.1		1,029.5
Marketable securities, Unrealized Gains	12.8		12.2
Marketable securities, Unrealized Losses	(0.9)		(3.0)
Marketable securities, Fair Value	1,093.0		1,038.7
Cash and marketables securities, Cost Basis	1,129.3		1,131.7
Total cash and marketable securities	1,141.2		1,140.9
Available-for-sale Securities, Activity [Abstract]
Proceeds from sales and maturities	188.1	314.0
Gross realized gains	1.6	1.9
Gross realized losses	0.3	1.3
Other-then-temporarily impairments on investments	0.3	0
Percentage of marketable securities maturing in 2012	14.10%
Percentage of marketable securities maturing in 2013	34.20%
Percentage of marketable securities maturing after 2013	51.70%
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investments with continuous unrealized losses, Less than 12 months, Fair Value	203.0		204.2
Investments with continuous unrealized losses, Less than 12 months, Unrealized Losses	(0.9)		(2.7)
Investments with continuous unrealized losses, Greater than 12 months, Fair Value	0		4.0
Investments with continuous unrealized losses, Greater than 12 months, Unrealized Losses	0		(0.3)
Investments with continuous unrealized losses, Total Fair Value	203.0		208.2
Investments with continuous unrealized losses, Total Unrealized Losses	(0.9)		(3.0)
U.S. government and agency securities [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	345.4		292.5
Marketable securities, Unrealized Gains	2.7		3.4
Marketable securities, Unrealized Losses	(0.3)		0
Marketable securities, Fair Value	347.8		295.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investments with continuous unrealized losses, Less than 12 months, Fair Value	95.6
Investments with continuous unrealized losses, Less than 12 months, Unrealized Losses	(0.3)
Investments with continuous unrealized losses, Greater than 12 months, Fair Value	0
Investments with continuous unrealized losses, Greater than 12 months, Unrealized Losses	0
Investments with continuous unrealized losses, Total Fair Value	95.6
Investments with continuous unrealized losses, Total Unrealized Losses	(0.3)
Foreign government bonds [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	22.3		24.9
Marketable securities, Unrealized Gains	0.6		0.5
Marketable securities, Unrealized Losses	0		0
Marketable securities, Fair Value	22.9		25.4
Asset-backed securities [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	84.0		58.2
Marketable securities, Unrealized Gains	0.4		0.1
Marketable securities, Unrealized Losses	0		(0.3)
Marketable securities, Fair Value	84.4		58.0
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investments with continuous unrealized losses, Less than 12 months, Fair Value			31.7
Investments with continuous unrealized losses, Less than 12 months, Unrealized Losses			(0.1)
Investments with continuous unrealized losses, Greater than 12 months, Fair Value			1.1
Investments with continuous unrealized losses, Greater than 12 months, Unrealized Losses			(0.2)
Investments with continuous unrealized losses, Total Fair Value			32.8
Investments with continuous unrealized losses, Total Unrealized Losses			(0.3)
Mortgage-backed securities [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	113.6		124.1
Marketable securities, Unrealized Gains	1.2		1.1
Marketable securities, Unrealized Losses	(0.1)		(0.3)
Marketable securities, Fair Value	114.7		124.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investments with continuous unrealized losses, Less than 12 months, Fair Value	21.4		35.1
Investments with continuous unrealized losses, Less than 12 months, Unrealized Losses	(0.1)		(0.2)
Investments with continuous unrealized losses, Greater than 12 months, Fair Value	0		1.9
Investments with continuous unrealized losses, Greater than 12 months, Unrealized Losses	0		(0.1)
Investments with continuous unrealized losses, Total Fair Value	21.4		37.0
Investments with continuous unrealized losses, Total Unrealized Losses	(0.1)		(0.3)
Corporate notes and bonds [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	500.9		518.0
Marketable securities, Unrealized Gains	7.8		7.0
Marketable securities, Unrealized Losses	(0.5)		(2.4)
Marketable securities, Fair Value	508.2		522.6
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Investments with continuous unrealized losses, Less than 12 months, Fair Value	86.0		137.4
Investments with continuous unrealized losses, Less than 12 months, Unrealized Losses	(0.5)		(2.4)
Investments with continuous unrealized losses, Greater than 12 months, Fair Value	0		1.0
Investments with continuous unrealized losses, Greater than 12 months, Unrealized Losses	0		0
Investments with continuous unrealized losses, Total Fair Value	86.0		138.4
Investments with continuous unrealized losses, Total Unrealized Losses	(0.5)		(2.4)
Municipal securities [Member]
Available-for-sale Securities, Current [Abstract]
Marketable securities, Cost Basis	14.9		11.8
Marketable securities, Unrealized Gains	0.1		0.1
Marketable securities, Unrealized Losses	0		0
Marketable securities, Fair Value	$ 15.0		$ 11.9