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, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	2,886	$	5	$	(2	)	$	2,889
Other government-related debt securities:
U.S.	963		1		(3		)	961
Foreign and other	1,547		26		(9		)	1,564
Corporate debt securities:
Financial	5,131		35		(3		)	5,163
Industrial	5,337		46		(10		)	5,373
Other	570		5		(1		)	574
Residential mortgage-backed securities	1,746		5		(11		)	1,740
Other mortgage- and asset-backed securities	1,926		1		(53		)	1,874
Money market mutual funds	3,328		—		—			3,328
Other short-term interest-bearing securities	2,138		—		—			2,138
Total interest-bearing securities	25,572		124		(92		)	25,604
Equity securities	86		—		(4		)	82
Total available-for-sale investments	$	25,658	$	124	$	(96	)	$	25,686



Type of security as of December 31, 2013	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
U.S. Treasury securities	$	4,737	$	2	$	(9	)	$	4,730
Other government-related debt securities:
U.S.	1,087		—		(8		)	1,079
Foreign and other	1,574		13		(41		)	1,546
Corporate debt securities:
Financial	3,667		28		(19		)	3,676
Industrial	3,745		36		(21		)	3,760
Other	388		4		(2		)	390
Residential mortgage-backed securities	1,478		3		(21		)	1,460
Other mortgage- and asset-backed securities	1,555		1		(45		)	1,511
Money market mutual funds	3,366		—		—			3,366
Other short-term interest-bearing securities	750		—		—			750
Total interest-bearing securities	22,347		87		(166		)	22,268
Equity securities	85		10		—			95
Total available-for-sale investments	$	22,432	$	97	$	(166	)	$	22,363

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, 2014		December 31, 2013
Cash and cash equivalents	$	3,768	$	3,266
Marketable securities	21,836		15,596
Other assets — noncurrent	82		95
Restricted investments	—		3,406
Total available-for-sale investments	$	25,686	$	22,363

Cash and cash equivalents in the table above excludes cash of $584 million and $539 million as of June 30, 2014, and December 31, 2013, respectively. Restricted investments in the table above excludes $6 million of interest receivable as of December 31, 2013.

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, 2014		December 31, 2013
Maturing in one year or less	$	5,820	$	6,799
Maturing after one year through three years	5,927		4,785
Maturing after three years through five years	7,394		6,057
Maturing after five years through ten years	2,671		1,656
Maturing after ten years	178		—
Mortgage- and asset-backed securities	3,614		2,971
Total interest-bearing securities	$	25,604	$	22,268

For the three months ended June 30, 2014 and 2013, realized gains totaled $57 million and $33 million, respectively, and realized losses totaled $17 million and $26 million, respectively. For the six months ended June 30, 2014 and 2013, realized gains totaled $85 million and $118 million, respectively, and realized losses totaled $43 million and $44 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, 2014	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	700	$	(1	)	$	280	$	(1	)
Other government-related debt securities:
U.S.	—		—			323		(3		)
Foreign and other	148		(2		)	277		(7		)
Corporate debt securities:
Financial	1,047		(2		)	134		(1		)
Industrial	1,831		(9		)	130		(1		)
Other	126		(1		)	—		—
Residential mortgage-backed securities	459		(3		)	462		(8		)
Other mortgage- and asset-backed securities	514		(5		)	860		(48		)
Equity securities	16		(4		)	—		—
Total	$	4,841	$	(27	)	$	2,466	$	(69	)



	Less than 12 months					12 months or greater
Type of security as of December 31, 2013	Fair value		Unrealized losses			Fair value		Unrealized losses
U.S. Treasury securities	$	2,362	$	(9	)	$	—	$	—
Other government-related debt securities:
U.S.	789		(8		)	—		—
Foreign and other	986		(38		)	39		(3		)
Corporate debt securities:
Financial	1,781		(19		)	—		—
Industrial	1,543		(21		)	1		—
Other	182		(2		)	—		—
Residential mortgage-backed securities	794		(14		)	257		(7		)
Other mortgage- and asset-backed securities	982		(29		)	313		(16		)
Total	$	9,419	$	(140	)	$	610	$	(26	)

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. As of June 30, 2014, and December 31, 2013, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.