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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Change in Asset Retirement Obligation [Table Text Block]
Changes in asset retirement obligations were as follows:
 
Year Ended December 31,
 
2012
 
2011
(millions)
 
 
 
Asset Retirement Obligations, Beginning Balance
$
377

 
$
253

Liabilities Incurred
43

 
23

Liabilities Settled
(112
)
 
(24
)
Revision of Estimate
102

 
105

Accretion Expense
22

 
20

Other
(30
)
 
—

Asset Retirement Obligations, Ending Balance
$
402

 
$
377