Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2016

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)	2016		2015
Commercial paper	$	31.0	$	21.9
Overnight reverse repurchase agreements	—		134.7
Money market funds	741.7		673.8
Short-term debt securities	1,266.9		79.1
Total	$	2,039.6	$	909.5

Marketable securities including strategic investments

As of December 31, 2016 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Corporate debt securities
Current	$	1,408.6	$	0.2	$	(0.6	)	$	1,409.0
Non-current	1,255.2		1.2		(4.7		)	1,258.7
Government securities
Current	1,156.0		0.2		(0.3		)	1,156.1
Non-current	1,016.5		0.5		(3.4		)	1,019.4
Mortgage and other asset backed securities
Current	4.0		—		—			4.0
Non-current	557.7		0.8		(2.2		)	559.1
Total marketable debt securities	$	5,398.0	$	2.9	$	(11.2	)	$	5,406.3
Marketable equity securities, non-current	$	24.9	$	0.7	$	(9.3	)	$	33.5

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

Summary of contractual maturities: Available-for-sale securities

	As of December 31, 2016				As of December 31, 2015
(In millions)	Estimated Fair  Value		Amortized Cost		Estimated Fair  Value		Amortized Cost
Due in one year or less	$	2,568.6	$	2,569.1	$	2,120.5	$	2,122.0
Due after one year through five years	2,552.6		2,559.7		2,575.9		2,583.9
Due after five years	276.8		277.5		184.5		185.3
Total available-for-sale securities	$	5,398.0	$	5,406.3	$	4,880.9	$	4,891.2

Proceeds from marketable securities, excluding strategic investments

	For the Years Ended December 31,
(In millions)	2016		2015		2014
Proceeds from maturities and sales	$	7,378.9	$	4,063.0	$	2,718.9
Realized gains	$	3.3	$	1.5	$	0.7
Realized losses	$	4.3	$	3.5	$	0.5