|**Allowance for Doubtful Accounts (Tables)**   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
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|**Allowance for Doubtful Accounts [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Changes in the allowance for doubtful accounts | Changes in the allowance for doubtful accounts were as follows:Year Ended December 31,(millions)201320122011Balance, Beginning of Period$10$9$27ChangesChanges in Ecuador Receivable, Net(1)——(19)Other Changes111Net Changes11(18)Balance, End of Period$11$10$9(1)During 2011, recovery of approximately$19 millionfor outstanding receivables was included in the final terms of our agreement to transfer our assets and the associated electricity concession and PSC to the Ecuadorian government. SeeNote 3.  Property Transactions.
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|(millions)                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Balance, Beginning of Period                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Changes                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Changes in Ecuador Receivable, Net(1)          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other Changes                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Net Changes                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Balance, End of Period                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
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|(1)                                            | During 2011, recovery of approximately$19 millionfor outstanding receivables was included in the final terms of our agreement to transfer our assets and the associated electricity concession and PSC to the Ecuadorian government. SeeNote 3.  Property Transactions.                                                                                                                                                                                                                                                                    

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