Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2014

Investments, All Other Investments [Abstract]

Marketable securities including strategic investments

As of December 31, 2014 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	370.4	$	—	$	(0.2	)	$	370.6
Non-current	692.6		0.2		(1.5		)	693.9
Government securities
Current	269.9		—		(0.1		)	270.0
Non-current	579.9		0.3		(0.4		)	580.0
Mortgage and other asset backed securities
Current	0.2		—		—			0.2
Non-current	198.1		0.2		(0.2		)	198.1
Total marketable debt securities	$	2,111.1	$	0.7	$	(2.4	)	$	2,112.8
Marketable equity securities, non-current	$	6.9	$	1.2	$	(0.2	)	$	5.9

As of December 31, 2013 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	100.7	$	—	$	—		$	100.7
Non-current	339.1		0.4		(0.1		)	338.8
Government securities
Current	519.5		—		—			519.5
Non-current	155.2		—		(0.1		)	155.3
Mortgage and other asset backed securities
Current	—		—		—			—
Non-current	131.4		—		(0.1		)	131.5
Total marketable debt securities	$	1,245.9	$	0.4	$	(0.3	)	$	1,245.8
Marketable equity securities, non-current	$	11.2	$	8.7	$	—		$	2.5

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

	As of December 31,
(In millions)	2014		2013
Commercial paper	$	54.2	$	1.2
Overnight reverse repurchase agreements	305.0		22.4
Money market funds	321.2		396.0
Short-term debt securities	35.9		5.1
Total	$	716.3	$	424.7

Summary of contractual maturities: Available-for-sale securities

	As of December 31, 2014				As of December 31, 2013
(In millions)	Estimated Fair  Value		Amortized Cost		Estimated Fair  Value		Amortized Cost
Due in one year or less	$	640.5	$	640.8	$	620.2	$	620.2
Due after one year through five years	1,343.7		1,345.2		573.1		572.9
Due after five years	126.9		126.8		52.6		52.7
Total available-for-sale securities	$	2,111.1	$	2,112.8	$	1,245.9	$	1,245.8

Proceeds from marketable securities, excluding strategic investments

	For the Years Ended December 31,
(In millions)	2014		2013		2012
Proceeds from maturities and sales	$	2,718.9	$	5,190.1	$	2,749.6
Realized gains	$	0.7	$	6.6	$	2.1
Realized losses	$	0.5	$	2.1	$	3.5