v2.4.0.6
Available-for-sale investments
 3 Months Ended
Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]  
Available-for-sale investments
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 March 31, 2013
 
Amortized
cost
 
Gross
unrealized
gains
 
Gross
unrealized
losses
 
Estimated
fair
value
U.S. Treasury securities
 
$
2,698

 
$
9

 
$
—

 
$
2,707

Other government-related debt securities:
 
 
 
 
 
 
 
 
U.S.
 
1,013

 
6

 
—

 
1,019

Foreign and other
 
1,436

 
35

 
(5
)
 
1,466

Corporate debt securities:
 
 
 
 
 
 
 
 
Financial
 
3,907

 
72

 
(2
)
 
3,977

Industrial
 
4,380

 
79

 
(2
)
 
4,457

Other
 
470

 
9

 
—

 
479

Residential mortgage-backed securities
 
1,816

 
9

 
(8
)
 
1,817

Other mortgage- and asset-backed securities
 
1,515

 
2

 
(20
)
 
1,497

Money market mutual funds
 
1,742

 
—

 
—

 
1,742

Other short-term interest-bearing securities
 
1,677

 
—

 
—

 
1,677

Total interest-bearing securities
 
20,654

 
221

 
(37
)
 
20,838

Equity securities
 
55

 
7

 
—

 
62

Total available-for-sale investments
 
$
20,709

 
$
228

 
$
(37
)
 
$
20,900


Type of security as of December 31, 2012
 
Amortized
cost
 
Gross
unrealized
gains
 
Gross
unrealized
losses
 
Estimated
fair
value
U.S. Treasury securities
 
$
4,443

 
$
15

 
$
—

 
$
4,458

Other government-related debt securities:
 
 
 
 
 
 
 
 
U.S.
 
1,018

 
12

 
—

 
1,030

Foreign and other
 
1,549

 
60

 
(1
)
 
1,608

Corporate debt securities:
 
 
 
 
 
 
 
 
Financial
 
3,266

 
96

 
(1
)
 
3,361

Industrial
 
4,283

 
100

 
(3
)
 
4,380

Other
 
441

 
11

 
—

 
452

Residential mortgage-backed securities
 
1,828

 
9

 
(8
)
 
1,829

Other mortgage- and asset-backed securities
 
1,769

 
7

 
(9
)
 
1,767

Money market mutual funds
 
2,620

 
—

 
—

 
2,620

Other short-term interest-bearing securities
 
2,186

 
—

 
—

 
2,186

Total interest-bearing securities
 
23,403

 
310

 
(22
)
 
23,691

Equity securities
 
52

 
2

 
—

 
54

Total available-for-sale investments
 
$
23,455

 
$
312

 
$
(22
)
 
$
23,745



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
 
March 31,
2013
 
December 31,
2012
Cash and cash equivalents
 
$
2,097

 
$
2,887

Marketable securities
 
18,741

 
20,804

Other assets — noncurrent
 
62

 
54

Total available-for-sale investments
 
$
20,900

 
$
23,745


Cash and cash equivalents in the table above excludes cash of $433 million and $370 million as of March 31, 2013, and December 31, 2012, 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
 
March 31,
2013
 
December 31,
2012
Maturing in one year or less
 
$
3,916

 
$
7,175

Maturing after one year through three years
 
4,926

 
5,014

Maturing after three years through five years
 
6,919

 
6,286

Maturing after five years through ten years
 
1,763

 
1,620

Mortgage- and asset-backed securities
 
3,314

 
3,596

Total interest-bearing securities
 
$
20,838

 
$
23,691


For the three months ended March 31, 2013 and 2012, realized gains totaled $85 million and $67 million, respectively, and realized losses totaled $18 million and $19 million, respectively. The cost of securities sold is based on the specific identification method.
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 March 31, 2013, and December 31, 2012, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.