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 consolidated balance sheets:



	As of December 31,
(In millions)	2018		2017
Commercial paper	$	231.2	$	30.5
Overnight reverse repurchase agreements	—		3.6
Money market funds	279.5		948.0
Short-term debt securities	194.8		247.3
Total	$	705.5	$	1,229.4

The carrying values of our commercial paper, including accrued interest, overnight reverse repurchase agreements, money market funds and our short-term debt securities approximate fair value due to their short-term maturities.

Upon the adoption of ASU 2016-01, our marketable equity securities gains (losses) are recorded in other income (expense), net in our consolidated statements of income. The following tables summarize our marketable debt and equity securities, classified as available for sale:



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



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 December 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	$	2,313.4	$	2,314.6	$	2,115.2	$	2,116.0
Due after one year through five years	1,232.7		1,235.9		2,730.0		2,730.0
Due after five years	143.2		143.5		327.3		327.0
Total available-for-sale securities	$	3,689.3	$	3,694.0	$	5,172.5	$	5,173.0

The average maturity of our marketable debt securities available-for-sale as of December 31, 2018 and 2017, were 12 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 Years Ended December 31,
(In millions)	2018		2017		2016
Proceeds from maturities and sales	$	9,173.7	$	5,565.9	$	7,378.9
Realized gains	$	3.2	$	3.0	$	3.3
Realized losses	$	11.7	$	22.4	$	4.3

Realized losses for the year ended December 31, 2018, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities. Realized losses for the year ended December 31, 2017, primarily relate to impairments recognized on certain of our available-for-sale marketable debt securities, sales of agency mortgage-backed securities, corporate bonds and government securities. Realized losses for the year ended December 31, 2016, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities.

Strategic Investments

As of December 31, 2018 and 2017, our strategic investment portfolio was comprised of investments totaling $676.3 million and $85.8 million, respectively, which are included in investments and other assets in our consolidated balance sheets. The increase in our strategic investment portfolio is primarily a result of our investment in Ionis' common stock, as discussed below.

Our strategic investment portfolio includes investments in equity securities of certain biotechnology companies and venture capital funds where the underlying investments are in equity securities of certain 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 marketable equity securities within our disclosures included in Note 8, Fair Value Measurements, to these consolidated financial statements.

Ionis Pharmaceuticals, Inc.

In June 2018 we closed a new 10-year exclusive agreement with Ionis to develop novel antisense oligonucleotide (ASO) drug candidates for a broad range of neurological diseases (the 2018 Ionis Agreement) for a total payment of $1.0 billion, consisting of an upfront payment of $375.0 million and the purchase of approximately 11.5 million shares of Ionis' common stock at a cost of $625.0 million.

Our investment in Ionis' common stock is remeasured each reporting period and carried at fair value as a Level 2 marketable equity security due to certain holding period restrictions. The effect of these holding period restrictions are estimated using an option pricing valuation model. The most significant assumptions within the model are the term of the restrictions and the stock price volatility, which is based upon historical volatility of similar companies. We also use a constant maturity risk-free interest rate to match the remaining term of the restrictions on our investment in Ionis' common stock and a dividend yield of zero based upon the fact that Ionis and similar companies generally have not historically granted cash dividends.

For additional information on the 2018 Ionis Agreement, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Samsung Bioepis

In June 2018 we exercised our option under our joint venture agreement with Samsung BioLogics to increase our ownership percentage in Samsung Bioepis from approximately 5% to approximately 49.9%. The share purchase transaction was completed in November 2018 and, upon closing, we paid 759.5 billion South Korean won ($676.6 million) to Samsung BioLogics.

As of December 31, 2018, the carrying value of our investment in Samsung Bioepis totaled 759.5 billion South Korean won ($680.6 million), which is classified as a component of investments and other assets within our consolidated balance sheet.

For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.