Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2013

Investments, All Other Investments [Abstract]

Marketable Debt and Equity Securities

As of June 30, 2013 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	26.4	$	—	$	—		$	26.4
Non-current	73.2		—		(0.2		)	73.4
Government securities
Current	248.8		—		—			248.8
Non-current	24.4		—		—			24.4
Mortgage and other asset backed securities
Current	—		—		—			—
Non-current	9.5		—		—			9.5
Total marketable debt securities	$	382.3	$	—	$	(0.2	)	$	382.5
Marketable equity securities, non-current	$	28.9	$	14.7	$	—		$	14.2

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 June 30, 2013		As of December 31, 2012
Commercial paper	$	10.3	$	40.7
Overnight repurchase agreements	—		67.4
Short-term debt securities	251.2		331.3
Total	$	261.5	$	439.4

Summary of Contractual Maturities: Available-for-Sale Securities

	As of June 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	$	275.2	$	275.3	$	1,135.0	$	1,134.5
Due after one year through five years	103.9		104.0		1,744.3		1,741.2
Due after five years	3.2		3.2		292.4		292.3
Total available-for-sale securities	$	382.3	$	382.5	$	3,171.7	$	3,168.0

Proceeds from Marketable Debt Securities

	For the Three Months Ended June 30,					For the Six Months Ended June 30,
(In millions)	2013		2012			2013			2012
Proceeds from maturities and sales	$	78.3	$	599.6		$	4,404.7		$	1,423.9
Realized gains	$	—	$	0.6		$	6.3		$	1.3
Realized losses	$	—	$	(1.3	)	$	(2.0	)	$	(2.0	)