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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2013
Table Text Block [Abstract]  
Asset Retirement Obligations Rollforward
The following summarizes changes in the Company’s AROs during 2013 and 2012:
millions
2013
 
2012
Carrying amount of asset retirement obligations at January 1
$
1,885

 
$
1,768

Liabilities incurred
182

 
70

Property dispositions
(76
)
 
(78
)
Liabilities settled
(162
)
 
(89
)
Accretion expense
110

 
110

Revisions in estimated liabilities
83

 
104

Carrying amount of asset retirement obligations at December 31
$
2,022

 
$
1,885