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Asset Retirement Obligations (Tables)
 3 Months Ended
Mar. 31, 2015
Asset Retirement Obligation [Abstract]  
Schedule of asset retirement obligations
The following table summarizes the Company's asset retirement obligation activity during the three months ended March 31, 2015 and 2014: 
 
 
Three Months Ended
March 31,
 
 
2015
 
2014
 
 
(in millions)
Beginning asset retirement obligations
 
$
189

 
$
194

New wells placed on production
 
1

 
1

Changes in estimates
 
—

 
1

Dispositions
 
—

 
(1
)
Liabilities settled
 
(5
)
 
(4
)
Accretion of discount
 
3

 
3

Ending asset retirement obligations
 
$
188

 
$
194