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, 2015	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	3,604	$	14	$	(8	)	$	3,610
Other government-related debt securities:
U.S.	551		1		(1		)	551
Foreign and other	1,718		19		(14		)	1,723
Corporate debt securities:
Financial	7,425		22		(21		)	7,426
Industrial	7,657		27		(55		)	7,629
Other	830		3		(4		)	829
Residential mortgage-backed securities	1,498		7		(8		)	1,497
Other mortgage- and asset-backed securities	2,053		1		(40		)	2,014
Money market mutual funds	2,951		—		—			2,951
Other short-term interest-bearing securities	1,284		—		—			1,284
Total interest-bearing securities	29,571		94		(151		)	29,514
Equity securities	97		82		(4		)	175
Total available-for-sale investments	$	29,668	$	176	$	(155	)	$	29,689



Type of security as of December 31, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	3,632	$	22	$	(8	)	$	3,646
Other government-related debt securities:
U.S.	530		1		(3		)	528
Foreign and other	1,572		21		(24		)	1,569
Corporate debt securities:
Financial	6,036		21		(16		)	6,041
Industrial	6,394		23		(66		)	6,351
Other	650		3		(4		)	649
Residential mortgage-backed securities	1,708		4		(10		)	1,702
Other mortgage- and asset-backed securities	1,837		—		(41		)	1,796
Money market mutual funds	3,004		—		—			3,004
Other short-term interest-bearing securities	1,302		—		—			1,302
Total interest-bearing securities	26,665		95		(172		)	26,588
Equity securities	98		48		(2		)	144
Total available-for-sale investments	$	26,763	$	143	$	(174	)	$	26,732

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, 2015		December 31, 2014
Cash and cash equivalents	$	3,316	$	3,293
Marketable securities	26,198		23,295
Other assets — noncurrent	175		144
Total available-for-sale investments	$	29,689	$	26,732

Cash and cash equivalents in the table above excludes cash of $479 million and $438 million as of June 30, 2015, and December 31, 2014, 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, 2015		December 31, 2014
Maturing in one year or less	$	4,701	$	4,936
Maturing after one year through three years	8,712		6,829
Maturing after three years through five years	8,900		7,840
Maturing after five years through ten years	3,468		3,267
Maturing after ten years	222		218
Mortgage- and asset-backed securities	3,511		3,498
Total interest-bearing securities	$	29,514	$	26,588

For the three months ended June 30, 2015 and 2014, realized gains totaled $18 million and $57 million, respectively, and realized losses totaled $27 million and $17 million, respectively. For the six months ended June 30, 2015 and 2014, realized gains totaled $54 million and $85 million, respectively, and realized losses totaled $98 million and $43 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, 2015	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	1,522	$	(7	)	$	30	$	(1	)
Other government-related debt securities:
U.S.	275		(1		)	20		—
Foreign and other	701		(12		)	71		(2		)
Corporate debt securities:
Financial	3,539		(20		)	156		(1		)
Industrial	4,364		(51		)	307		(4		)
Other	358		(4		)	24		—
Residential mortgage-backed securities	464		(3		)	305		(5		)
Other mortgage- and asset-backed securities	1,020		(11		)	401		(29		)
Equity securities	—		—			2		(4		)
Total	$	12,243	$	(109	)	$	1,316	$	(46	)



	Less than 12 months					12 months or greater
Type of security as of December 31, 2014	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	1,770	$	(7	)	$	171	$	(1	)
Other government-related debt securities:
U.S.	160		—			178		(3		)
Foreign and other	514		(14		)	159		(10		)
Corporate debt securities:
Financial	3,150		(14		)	158		(2		)
Industrial	3,931		(62		)	222		(4		)
Other	354		(4		)	5		—
Residential mortgage-backed securities	614		(4		)	413		(6		)
Other mortgage- and asset-backed securities	1,071		(8		)	561		(33		)
Equity securities	5		(2		)	—		—
Total	$	11,569	$	(115	)	$	1,867	$	(59	)

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 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. This 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 due to new developments or changes in assumptions related to any particular security. As of June 30, 2015, and December 31, 2014, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.