The amortized cost, gross unrealized gains, gross unrealized losses and fair values of interest-bearing securities, all of which are considered available-for-sale, by type of security were as follows (in millions):



Types of securities as of December 31, 2019	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair values
U.S. Treasury notes	$	359	$	1	$	—	$	360
U.S. Treasury bills	—		—		—		—
Other government-related debt securities:
U.S.	—		—		—		—
Foreign and other	—		—		—		—
Corporate debt securities:
Financial	1,108		13		—		1,121
Industrial	824		10		—		834
Other	195		3		—		198
Residential-mortgage-backed securities	181		1		—		182
Other mortgage- and asset-backed securities	—		—		—		—
Money market mutual funds	5,250		—		—		5,250
Other short-term interest-bearing securities	289		—		—		289
Total available-for-sale investments	$	8,206	$	28	$	—	$	8,234



Types of securities as of December 31, 2018	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair values
U.S. Treasury notes	$	2,710	$	—	$	(47	)	$	2,663
U.S. Treasury bills	8,191		—		—			8,191
Other government-related debt securities:
U.S.	112		—		(2		)	110
Foreign and other	972		1		(41		)	932
Corporate debt securities:
Financial	2,778		—		(81		)	2,697
Industrial	2,603		—		(99		)	2,504
Other	583		—		(21		)	562
Residential-mortgage-backed securities	1,458		—		(36		)	1,422
Other mortgage- and asset-backed securities	483		—		(14		)	469
Money market mutual funds	5,659		—		—			5,659
Other short-term interest-bearing securities	3,515		—		—			3,515
Total available-for-sale investments	$	29,064	$	1	$	(341	)	$	28,724



	December 31,
Consolidated Balance Sheets locations	2019		2018
Cash and cash equivalents	$	5,360	$	6,365
Marketable securities	2,874		22,359
Total available-for-sale investments	$	8,234	$	28,724



	December 31,
Contractual maturities	2019		2018
Maturing in one year or less	$	5,629	$	17,424
Maturing after one year through three years	2,304		3,356
Maturing after three years through five years	119		5,168
Maturing after five years through ten years	—		885
Mortgage- and asset-backed securities	182		1,891
Total available-for-sale investments	$	8,234	$	28,724

For the years ended December 31, 2019, 2018 and 2017, realized gains on interest-bearing securities were $92 million, $29 million and $147 million, respectively, and realized losses on interest-bearing securities were $36 million, $394 million and $213 million, respectively. Realized gains and losses on interest-bearing securities are recorded in Interest and other income, net, in the Consolidated Statements of Income. The cost of securities sold is based on the specific-identification method.

As of December 31, 2019, aggregate gross unrealized losses of available-for-sale investments were not material. As of December 31, 2018, the fair values and gross unrealized losses of available-for-sale investments in an unrealized loss position aggregated by type and length of time that the securities have been in a continuous loss position were as follows (in millions):



	Less than 12 months					12 months or more
Types of securities as of December 31, 2018	Fair values		Unrealized losses			Fair values		Unrealized losses
U.S. Treasury notes	$	1,219	$	(21	)	$	1,444	$	(26	)
Other government-related debt securities:
U.S.	—		—			110		(2		)
Foreign and other	631		(31		)	240		(10		)
Corporate debt securities:
Financial	1,968		(59		)	718		(22		)
Industrial	1,898		(81		)	529		(18		)
Other	529		(20		)	28		(1		)
Residential-mortgage-backed securities	576		(14		)	840		(22		)
Other mortgage- and asset-backed securities	17		—			451		(14		)
Total	$	6,838	$	(226	)	$	4,360	$	(115	)

The primary objective of our investment portfolio is to maintain safety of principal, prudent levels of liquidity and acceptable levels of risk. Our investment policy limits interest-bearing security investments to certain types of debt and money market instruments issued by institutions with primarily investment-grade credit ratings, and it places restrictions on maturities and concentration by asset class and issuer.

We review our available-for-sale investments for other-than-temporary declines in fair value below our cost basis each quarter and whenever events or changes in circumstances indicate that the cost basis of an asset may not be recoverable. The evaluation is based on a number of factors, including the length of time and the extent to which the fair value has been below our cost basis as well as adverse conditions related specifically to the security, such as any changes to the credit rating of the security and the intent to sell or whether we will more likely than not be required to sell the security before recovery of its amortized cost basis. Our assessment of whether a security is other-than-temporarily impaired could change in the future based on new developments or changes in assumptions related to that particular security. As of December 31, 2019 and 2018, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.

We held investments in equity securities with readily determinable fair values of $303 million and $176 million as of December 31, 2019 and 2018, respectively, which are included in Other assets in the Consolidated Balance Sheets. Gains and losses recognized on equity securities with readily determinable fair values, including gains and losses recognized on sales, were not material for the years ended December 31, 2019, 2018 and 2017.

We held investments of $176 million and $222 million in equity securities without readily determinable fair values as of December 31, 2019 and 2018, respectively, which are included in Other assets in the Consolidated Balance Sheets. Adjustments to the carrying values of these securities were not material for the years ended December 31, 2019, 2018 and 2017.

We held limited partnership investments of $320 million and $285 million as of December 31, 2019 and 2018, respectively, which are included in Other assets in the Consolidated Balance Sheets. These investments are measured by using the net asset values of the underlying investments as a practical expedient. These investments are typically redeemable only through distributions upon liquidation of the underlying assets. As of December 31, 2019, unfunded additional commitments to be made for these investments during the next several years were not material. Gains and losses recognized on our limited partnership investments were not material for the years ended December 31, 2019, 2018 and 2017.