v2.4.0.6
Available-for-sale investments
 12 Months Ended
Dec. 31, 2012
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 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


Type of security as of December 31, 2011
Amortized
cost
 
Gross
unrealized
gains
 
Gross
unrealized
losses
 
Estimated
fair value
U.S. Treasury securities
$
3,878

 
$
68

 
$
—

 
$
3,946

Other government-related debt securities:
 
 
 
 
 
 
 
U.S.
1,548

 
23

 
—

 
1,571

Foreign and other
441

 
9

 
—

 
450

Corporate debt securities:
 
 
 
 
 
 
 
Financial
2,493

 
30

 
(15
)
 
2,508

Industrial
3,077

 
79

 
(10
)
 
3,146

Other
280

 
9

 
—

 
289

Residential mortgage-backed securities
518

 
3

 
(3
)
 
518

Other mortgage- and asset-backed securities
1,271

 
3

 
(7
)
 
1,267

Money market mutual funds
6,266

 
—

 
—

 
6,266

Total interest-bearing securities
19,772

 
224

 
(35
)
 
19,961

Equity securities
42

 
—

 
—

 
42

Total available-for-sale investments
$
19,814

 
$
224

 
$
(35
)
 
$
20,003


The fair values of available-for-sale investments by classification in the Consolidated Balance Sheets were as follows as of December 31, 2012 and 2011 (in millions):
Classification in the Consolidated Balance Sheets
2012
 
2011
Cash and cash equivalents
$
2,887

 
$
6,266

Marketable securities
20,804

 
13,695

Other assets — noncurrent
54

 
42

Total available-for-sale investments
$
23,745

 
$
20,003


Cash and cash equivalents in the table above excludes cash of $370 million and $680 million as of December 31, 2012 and 2011, 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 as of December 31, 2012 and 2011 (in millions):
Contractual maturity
2012
 
2011
Maturing in one year or less
$
7,175

 
$
6,791

Maturing after one year through three years
5,014

 
5,855

Maturing after three years through five years
6,286

 
5,379

Maturing after five years through ten years
1,620

 
151

Mortgage- and asset-backed securities
3,596

 
1,785

Total interest-bearing securities
$
23,691

 
$
19,961


For the years ended December 31, 2012, 2011 and 2010, realized gains totaled $186 million, $191 million and $115 million, respectively, and realized losses totaled $54 million, $37 million and $25 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 December 31, 2012 and 2011, we believe the cost bases for our available-for-sale investments were recoverable in all material respects.