Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2015

Investments, All Other Investments [Abstract]

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

	As of December 31,
(In millions)	2015		2014
Commercial paper	$	21.9	$	54.2
Overnight reverse repurchase agreements	134.7		305.0
Money market funds	673.8		321.2
Short-term debt securities	79.1		35.9
Total	$	909.5	$	716.3

Marketable securities including strategic investments

As of December 31, 2015 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Corporate debt securities
Current	$	394.3	$	—	$	(0.5	)	$	394.8
Non-current	1,116.6		0.1		(4.1		)	1,120.6
Government securities
Current	1,723.4		0.1		(1.1		)	1,724.4
Non-current	1,152.5		—		(3.1		)	1,155.6
Mortgage and other asset backed securities
Current	2.8		—		—			2.8
Non-current	491.3		0.1		(1.8		)	493.0
Total marketable debt securities	$	4,880.9	$	0.3	$	(10.6	)	$	4,891.2
Marketable equity securities, non-current	$	37.5	$	9.2	$	—		$	28.3

As of December 31, 2014 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
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

Summary of contractual maturities: Available-for-sale securities

	As of December 31, 2015				As of December 31, 2014
(In millions)	Estimated Fair  Value		Amortized Cost		Estimated Fair  Value		Amortized Cost
Due in one year or less	$	2,120.5	$	2,122.0	$	640.5	$	640.8
Due after one year through five years	2,575.9		2,583.9		1,343.7		1,345.2
Due after five years	184.5		185.3		126.9		126.8
Total available-for-sale securities	$	4,880.9	$	4,891.2	$	2,111.1	$	2,112.8

Proceeds from marketable securities, excluding strategic investments

	For the Years Ended December 31,
(In millions)	2015		2014		2013
Proceeds from maturities and sales	$	4,063.0	$	2,718.9	$	5,190.1
Realized gains	$	1.5	$	0.7	$	6.6
Realized losses	$	3.5	$	0.5	$	2.1