UNITED STATES STEEL CORP | 2013 | FY | 3

Amortizable intangible assets are amortized on a straight-line basis over their estimated useful lives and are detailed below:

 
 
 
 
As of December 31, 2013
 
As of December 31, 2012
(In millions)
 
Useful
Lives
 
Gross
Carrying
Amount
 
Accumulated
Amortization
 
Net
Amount
 
Gross
Carrying
Amount
 
Accumulated
Amortization
 
Net
Amount
Customer relationships
 
22-23 Years
 
$
215

 
$
63

 
$
152

 
$
221

 
$
54

 
$
167

Other
 
2-20 Years
 
23

 
12

 
11

 
22

 
11

 
11

Total amortizable intangible assets
 
 
 
$
238

 
$
75

 
$
163

 
$
243

 
$
65

 
$
178

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