Available-for-sale investments

The amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security were as follows (in millions):



Type of security as of June 30, 2017	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	7,664	$	9	$	(12	)	$	7,661
Other government-related debt securities:
U.S.	226		1		(1		)	226
Foreign and other	2,334		27		(8		)	2,353
Corporate debt securities:
Financial	9,591		56		(10		)	9,637
Industrial	9,499		88		(18		)	9,569
Other	1,229		8		(2		)	1,235
Residential mortgage-backed securities	1,689		1		(8		)	1,682
Other mortgage- and asset-backed securities	1,854		2		(3		)	1,853
Money market mutual funds	2,165		—		—			2,165
Other short-term interest-bearing securities	2,382		—		—			2,382
Total interest-bearing securities	38,633		192		(62		)	38,763
Equity securities	134		30		(5		)	159
Total available-for-sale investments	$	38,767	$	222	$	(67	)	$	38,922



Type of security as of December 31, 2016	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	6,681	$	1	$	(68	)	$	6,614
Other government-related debt securities:
U.S.	302		—		(3		)	299
Foreign and other	1,784		9		(34		)	1,759
Corporate debt securities:
Financial	8,476		21		(37		)	8,460
Industrial	8,793		59		(63		)	8,789
Other	1,079		5		(7		)	1,077
Residential mortgage-backed securities	1,968		1		(29		)	1,940
Other mortgage- and asset-backed securities	1,731		1		(13		)	1,719
Money market mutual funds	2,782		—		—			2,782
Other short-term interest-bearing securities	4,188		—		—			4,188
Total interest-bearing securities	37,784		97		(254		)	37,627
Equity securities	127		31		(4		)	154
Total available-for-sale investments	$	37,911	$	128	$	(258	)	$	37,781

The fair values of available-for-sale investments by classification in the Condensed Consolidated Balance Sheets were as follows (in millions):



Classification in the Condensed Consolidated Balance Sheets	June 30, 2017		December 31, 2016
Cash and cash equivalents	$	2,165	$	2,783
Marketable securities	36,598		34,844
Other noncurrent assets	159		154
Total available-for-sale investments	$	38,922	$	37,781

Cash and cash equivalents in the above table excludes bank account cash of $464 million and $458 million as of June 30, 2017 and December 31, 2016, respectively.

The fair values of available-for-sale interest-bearing security investments by contractual maturity, except for mortgage- and asset-backed securities that do not have a single maturity date, were as follows (in millions):



Contractual maturity	June 30, 2017		December 31, 2016
Maturing in one year or less	$	6,905	$	8,393
Maturing after one year through three years	11,629		10,404
Maturing after three years through five years	13,346		12,157
Maturing after five years through ten years	3,286		2,974
Maturing after ten years	62		40
Mortgage- and asset-backed securities	3,535		3,659
Total interest-bearing securities	$	38,763	$	37,627

For the three months ended June 30, 2017 and 2016, realized gains totaled $40 million and $31 million, respectively, and realized losses totaled $87 million and $54 million, respectively. For the six months ended June 30, 2017 and 2016, realized gains totaled $75 million and $68 million, respectively, and realized losses totaled $171 million and $121 million, respectively. The cost of securities sold is based on the specific identification method.

The unrealized losses on available-for-sale investments and their related fair values were as follows (in millions):



	Less than 12 months					12 months or greater
Type of security as of June 30, 2017	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	5,784	$	(12	)	$	—	$	—
Other government-related debt securities:
U.S.	132		(1		)	—		—
Foreign and other	968		(8		)	11		—
Corporate debt securities:
Financial	2,231		(9		)	22		(1		)
Industrial	2,646		(18		)	62		—
Other	370		(2		)	5		—
Residential mortgage-backed securities	1,355		(6		)	69		(2		)
Other mortgage- and asset-backed securities	917		(3		)	8		—
Equity securities	20		(5		)	—		—
Total	$	14,423	$	(64	)	$	177	$	(3	)



	Less than 12 months					12 months or greater
Type of security as of December 31, 2016	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	5,774	$	(68	)	$	—	$	—
Other government-related debt securities:
U.S.	201		(3		)	—		—
Foreign and other	1,192		(34		)	17		—
Corporate debt securities:
Financial	3,975		(37		)	44		—
Industrial	3,913		(61		)	149		(2		)
Other	486		(7		)	7		—
Residential mortgage-backed securities	1,631		(26		)	158		(3		)
Other mortgage- and asset-backed securities	1,087		(10		)	118		(3		)
Equity securities	22		(4		)	—		—
Total	$	18,281	$	(250	)	$	493	$	(8	)

The primary objective of our investment portfolio is to enhance overall returns in an efficient manner while maintaining 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 and adverse conditions related specifically to the security, including 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 June 30, 2017 and December 31, 2016, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.