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Asset Retirement Obligations (Tables)
 3 Months Ended
Mar. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]  
Changes in Asset Retirement Obligations
Changes in ARO are as follows:
 
Three Months Ended
March 31,
(millions)
2014
 
2013
Asset Retirement Obligations, Beginning Balance
$
586

 
$
402

Liabilities Incurred
1

 
1

Liabilities Settled
(14
)
 
(10
)
Revision of Estimate
72

 
(1
)
Accretion Expense (1)
10

 
7

Asset Retirement Obligations, Ending Balance
$
655

 
$
399


(1) Accretion expense is included in DD&A expense in the consolidated statements of operations.