Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2012

Investments, All Other Investments [Abstract]

Marketable Debt and Equity Securities

As of September 30, 2012 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	302.8	$	0.4	$	(0.1	)	$	302.5
Non-current	611.9		3.3		(0.2		)	608.8
Government securities
Current	845.6		0.4		—			845.2
Non-current	694.3		0.9		—			693.4
Mortgage and other asset backed securities
Current	5.7		—		—			5.7
Non-current	435.3		1.6		(1.1		)	434.8
Total marketable debt securities	$	2,895.6	$	6.6	$	(1.4	)	$	2,890.4
Marketable equity securities, non-current	$	1.2	$	—	$	—		$	1.2

As of December 31, 2011 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized 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

(In millions)	As of September 30, 2012		As of December 31, 2011
Commercial paper	$	16.3	$	—
Repurchase agreements	108.7		8.8
Short-term debt securities	184.0		391.0
Total	$	309.0	$	399.8

Summary of Contractual Maturities: Available-for-Sale Securities

	As of September 30, 2012				As of December 31, 2011
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,154.0	$	1,153.4	$	1,176.1	$	1,175.6
Due after one year through five years	1,529.8		1,525.5		1,251.6		1,251.4
Due after five years	211.8		211.5		165.2		165.8
Total available-for-sale securities	$	2,895.6	$	2,890.4	$	2,592.9	$	2,592.8

Proceeds from Marketable Debt Securities

	For the Three Months Ended September 30,						For the Nine Months Ended September 30,
(In millions)	2012			2011			2012			2011
Proceeds from maturities and sales	$	491.3		$	306.2		$	1,913.4		$	1,476.1
Realized gains	$	0.4		$	0.3		$	1.7		$	3.4
Realized losses	$	(0.8	)	$	(0.4	)	$	(2.7	)	$	(1.7	)