Financial Instruments

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 March 31, 2018		As of December 31, 2017
Commercial paper	$	51.5	$	30.5
Overnight reverse repurchase agreements	—		3.6
Money market funds	3,561.2		948.0
Short-term debt securities	161.0		247.3
Total	$	3,773.7	$	1,229.4

The carrying values of our commercial paper, including accrued interest, overnight reverse repurchase agreements, money market funds and short-term debt securities approximate fair value due to their short-term maturities. Upon adoption of ASU 2016-01, our marketable equity securities gains (losses) are recorded in other income (expense), net in our condensed consolidated statements of income.

The following tables summarize our marketable debt and equity securities, classified as available-for-sale:



As of March 31, 2018 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Corporate debt securities
Current	$	912.9	$	—	$	(0.8	)	$	913.7
Non-current	645.0		0.3		(0.7		)	645.4
Government securities
Current	895.0		—		(0.5		)	895.5
Non-current	248.2		0.1		(0.3		)	248.4
Mortgage and other asset backed securities
Current	0.1		—		—			0.1
Non-current	307.0		0.1		(1.0		)	307.9
Total marketable debt securities	$	3,008.2	$	0.5	$	(3.3	)	$	3,011.0



As of December 31, 2017 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Corporate debt securities
Current	$	1,039.3	$	—	$	(0.2	)	$	1,039.5
Non-current	1,570.5		0.9		—			1,569.6
Government securities
Current	1,075.1		0.1		(0.7		)	1,075.7
Non-current	844.2		0.2		(1.1		)	845.1
Mortgage and other asset backed securities
Current	0.8		—		—			0.8
Non-current	642.6		1.1		(0.8		)	642.3
Total marketable debt securities	$	5,172.5	$	2.3	$	(2.8	)	$	5,173.0
Marketable equity securities, non-current	$	11.8	$	1.8	$	(4.4	)	$	14.4

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 March 31, 2018				As of December 31, 2017
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,808.0	$	1,809.3	$	2,115.2	$	2,116.0
Due after one year through five years	1,123.0		1,124.2		2,730.0		2,730.0
Due after five years	77.2		77.5		327.3		327.0
Total available-for-sale securities	$	3,008.2	$	3,011.0	$	5,172.5	$	5,173.0

The average maturity of our marketable debt securities available-for-sale as of March 31, 2018 and December 31, 2017, was approximately 7 months and 17 months, respectively.

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 March 31,
(In millions)	2018			2017
Proceeds from maturities and sales	$	4,068.9		$	1,884.3
Realized gains	$	1.8		$	1.2
Realized losses	$	(9.4	)	$	(1.9	)

Strategic Investments

As of March 31, 2018 and December 31, 2017, our strategic investment portfolio was comprised of investments totaling $81.6 million and $85.8 million, respectively, which are included in investments and other assets in our condensed consolidated balance sheets. Our strategic investment portfolio includes investments in equity securities of certain biotechnology companies and investments in venture capital funds where the underlying investments are in equity securities of biotechnology companies. Our investments in equity securities of certain publicly-traded biotechnology companies are regularly measured and carried at fair value and classified as Level 1 assets.