|**Asset Retirement Obligations (Tables)**                            | 12 Months Ended                                                                                                                                                                                                                                                                                                          
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|**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 31,20122011(millions)Asset Retirement Obligations, Beginning Balance$377$253Liabilities Incurred4323Liabilities Settled(112)(24)Revision of Estimate102105Accretion Expense2220Other(30)—Asset Retirement Obligations, Ending Balance$402$377
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|                                                                     | Year Ended December 31,                                                                                                                                                                                                                                                                                                  
|                                                                     | 2012                                                                                                                                                                                                                                                                                                                     
|(millions)                                                           |                                                                                                                                                                                                                                                                                                                          
|Asset Retirement Obligations, Beginning Balance                      | $                                                                                                                                                                                                                                                                                                                        
|Liabilities Incurred                                                 | 43                                                                                                                                                                                                                                                                                                                       
|Liabilities Settled                                                  | (112                                                                                                                                                                                                                                                                                                                     
|Revision of Estimate                                                 | 102                                                                                                                                                                                                                                                                                                                      
|Accretion Expense                                                    | 22                                                                                                                                                                                                                                                                                                                       
|Other                                                                | (30                                                                                                                                                                                                                                                                                                                      
|Asset Retirement Obligations, Ending Balance                         | $                                                                                                                                                                                                                                                                                                                        

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                    duration X- DefinitionTabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation.+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859+ Details**Name:**
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