Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2013

Investments, All Other Investments [Abstract]

Marketable Debt and Equity Securities

As of September 30, 2013 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	76.7	$	—	$	—		$	76.7
Non-current	210.3		0.3		(0.1		)	210.1
Government securities
Current	164.2		—		—			164.2
Non-current	103.0		—		(0.1		)	103.1
Mortgage and other asset backed securities
Current	—		—		—			—
Non-current	60.2		—		(0.1		)	60.3
Total marketable debt securities	$	614.4	$	0.3	$	(0.3	)	$	614.4
Marketable equity securities, non-current	$	40.3	$	24.3	$	—		$	16.0

As of December 31, 2012 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	346.9	$	0.3	$	—		$	346.6
Non-current	654.1		2.8		(0.6		)	651.9
Government securities
Current	783.4		0.3		—			783.1
Non-current	874.4		0.8		—			873.6
Mortgage and other asset backed securities
Current	4.8		—		—			4.8
Non-current	508.1		1.4		(1.3		)	508.0
Total marketable debt securities	$	3,171.7	$	5.6	$	(1.9	)	$	3,168.0
Marketable equity securities, non-current	$	9.0	$	3.0	$	—		$	6.0

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

(In millions)	As of September 30, 2013		As of December 31, 2012
Commercial paper	$	12.0	$	40.7
Overnight repurchase agreements	35.5		67.4
Short-term debt securities	239.7		331.3
Total	$	287.2	$	439.4

Summary of Contractual Maturities: Available-for-Sale Securities

	As of September 30, 2013				As of December 31, 2012
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	240.9	$	240.9	$	1,135.0	$	1,134.5
Due after one year through five years	351.8		351.6		1,744.3		1,741.2
Due after five years	21.7		21.9		292.4		292.3
Total available-for-sale securities	$	614.4	$	614.4	$	3,171.7	$	3,168.0

Proceeds from Marketable Debt Securities

	For the Three Months Ended September 30,					For the Nine Months Ended September 30,
(In millions)	2013		2012			2013			2012
Proceeds from maturities and sales	$	617.5	$	491.3		$	5,025.2		$	1,913.4
Realized gains	$	0.2	$	0.4		$	6.6		$	1.7
Realized losses	$	—	$	(0.8	)	$	(2.1	)	$	(2.7	)