Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2019

Investments, Debt and Equity Securities [Abstract]

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

The following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included in cash and cash equivalents in our condensed consolidated balance sheets:

(In millions)	As of June 30, 2019		As of December 31, 2018
Commercial paper	$	338.7	$	231.2
Overnight reverse repurchase agreements	97.0		—
Money market funds	405.7		279.5
Short-term debt securities	279.0		194.8
Total	$	1,120.4	$	705.5

Marketable debt and equity securities

The following tables summarize our marketable debt and equity securities:

As of June 30, 2019 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	933.4	$	1.1	$	—		$	934.5
Non-current	748.9		4.4		(0.1		)	753.2
Government securities
Current	293.6		0.4		—			294.0
Non-current	309.7		0.9		(0.2		)	310.4
Mortgage and other asset backed securities
Current	0.3		—		—			0.3
Non-current	244.5		1.5		(0.3		)	245.7
Total marketable debt securities	$	2,530.4	$	8.3	$	(0.6	)	$	2,538.1
Marketable equity securities
Current	$	117.9	$	46.3	$	—		$	164.2
Non-current	111.4		247.9		(13.5		)	345.8
Total marketable equity securities	$	229.3	$	294.2	$	(13.5	)	$	510.0

As of December 31, 2018 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	1,608.4	$	—	$	(0.9	)	$	1,607.5
Non-current	854.9		0.7		(3.9		)	851.7
Government securities
Current	706.1		0.1		(0.4		)	705.8
Non-current	264.0		0.1		(0.3		)	263.8
Mortgage and other asset backed securities
Current	0.1		—		—			0.1
Non-current	260.5		0.4		(0.5		)	260.4
Total marketable debt securities	$	3,694.0	$	1.3	$	(6.0	)	$	3,689.3
Marketable equity securities, non-current	$	496.2	$	127.7	$	(8.5	)	$	615.4

Summary of contractual maturities: available-for-sale securities

The estimated fair value and amortized cost of our marketable debt securities available-for-sale by contractual maturity are summarized as follows:

	As of June 30, 2019				As of December 31, 2018
(In millions)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	1,227.3	$	1,228.8	$	2,314.6	$	2,313.4
Due after one year through five years	1,196.1		1,202.2		1,235.9		1,232.7
Due after five years	107.0		107.1		143.5		143.2
Total available-for-sale securities	$	2,530.4	$	2,538.1	$	3,694.0	$	3,689.3

Proceeds from marketable debt securities

The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows:

	For the Three Months Ended June 30,						For the Six Months Ended June 30,
(In millions)	2019			2018			2019			2018
Proceeds from maturities and sales	$	1,766.6		$	2,733.7		$	3,255.8		$	6,802.7
Realized gains	$	1.0		$	0.8		$	1.6		$	2.6
Realized losses	$	(0.3	)	$	(0.8	)	$	(0.6	)	$	(10.2	)