Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2012

Financial Instruments [Abstract]

Marketable Debt and Equity Securities

			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of March 31, 2012 (In millions):	Value		Gains		Losses			Cost
Available-for-sale:
Corporate debt securities
Current	$	227.3	$	0.3	$	(0.1	)	$	227.1
Non-current		498.6		2.3		(0.3	)		496.6
Government securities
Current		750.8		0.3		(0.1	)		750.6
Non-current		617.8		0.9		(0.1	)		617.0
Mortgage and other asset backed securities
Current		0.3		—		—			0.3
Non-current		355.6		1.0		(1.2	)		355.8
Total marketable debt securities	$	2,450.4	$	4.8	$	(1.8	)	$	2,447.4
Marketable equity securities, non-current	$	0.1	$	—	$	—		$	0.1
			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of December 31, 2011 (In millions):	Value		Gains		Losses			Cost
Available-for-sale:
Corporate debt securities
Current	$	155.0	$	0.2	$	(0.1	)	$	154.9
Non-current		447.6		1.2		(1.5	)		447.9
Government securities
Current		1,021.0		0.4		—			1,020.6
Non-current		695.5		0.9		(0.2	)		694.8
Mortgage and other asset backed securities
Current		0.1		—		—			0.1
Non-current		273.7		0.5		(1.3	)		274.5
Total marketable debt securities	$	2,592.9	$	3.2	$	(3.1	)	$	2,592.8
Marketable equity securities, non-current	$	0.1	$	—	$	(0.1	)	$	0.2

Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents

	As of		As of
	March 31,		December 31,
(In millions)	2012		2011
Repurchase agreements		14.4		8.8
Short-term debt securities		147.0		391.0
Total	$	161.4	$	399.8

Summary of Contractual Maturities: Available-for-Sale Securities

	As of March 31, 2012				As of December 31, 2011
	Estimated		Amortized		Estimated		Amortized
(In millions)	Fair Value		Cost		Fair Value		Cost
Due in one year or less	$	978.4	$	978.0	$	1,176.1	$	1,175.6
Due after one year through five years		1,280.8		1,278.0		1,251.6		1,251.4
Due after five years		191.2		191.4		165.2		165.8
Total available-for-sale securities	$	2,450.4	$	2,447.4	$	2,592.9	$	2,592.8

Proceeds from Marketable Debt Securities

	For the Three Months Ended March 31,
(In millions)	2012			2011
Proceeds from maturities and sales	$	824.4		$	788.1
Realized gains	$	0.7		$	2.4
Realized losses	$	(0.7	)	$	(0.8	)