|**Acquisitions and Divestitures (Tables)**                                                  | 12 Months Ended                                                                                                                                                                                                                                                                                               
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|**Acquisitions and Divestitures [Abstract]**                                                |                                                                                                                                                                                                                                                                                                               
|Sale of Onshore US Assets                                                                   | Summarized results of discontinued operations are as follows:Year Ended December 31,201220112010(millions)Oil and Gas Sales$208$357$309Income Before Income Taxes101215183Income Tax Expense5517489Operating Income, Net of Tax464194Gain on Sale, Net of Tax16——Discontinued Operations, Net of Tax$62$41$94 
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|                                                                                            |                                                                                                                                                                                                                                                                                                               
|                                                                                            | Year Ended December 31,                                                                                                                                                                                                                                                                                       
|                                                                                            | 2012                                                                                                                                                                                                                                                                                                          
|(millions)                                                                                  |                                                                                                                                                                                                                                                                                                               
|Oil and Gas Sales                                                                           | $                                                                                                                                                                                                                                                                                                             
|Income Before Income Taxes                                                                  | 101                                                                                                                                                                                                                                                                                                           
|Income Tax Expense                                                                          | 55                                                                                                                                                                                                                                                                                                            
|Operating Income, Net of Tax                                                                | 46                                                                                                                                                                                                                                                                                                            
|Gain on Sale, Net of Tax                                                                    | 16                                                                                                                                                                                                                                                                                                            
|Discontinued Operations, Net of Tax                                                         | $                                                                                                                                                                                                                                                                                                             
|Schedule of Disposal Groups, Gain on Divestitures - Onshore US [Table Text Block]           | The information regarding the assets sold is as follows:Year Ended December 31,2012(millions)Cash Proceeds$1,044LessNet Book Value of Assets Sold(836)Goodwill Allocated to Assets Sold(61)Asset Retirement Obligations Associated with Assets Sold20Other Closing Adjustments(13)Gain on Divestitures$154    
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|                                                                                            |                                                                                                                                                                                                                                                                                                               
|                                                                                            | Year Ended December 31,                                                                                                                                                                                                                                                                                       
|                                                                                            | 2012                                                                                                                                                                                                                                                                                                          
|(millions)                                                                                  |                                                                                                                                                                                                                                                                                                               
|Cash Proceeds                                                                               | $                                                                                                                                                                                                                                                                                                             
|Less                                                                                        |                                                                                                                                                                                                                                                                                                               
|Net Book Value of Assets Sold                                                               | (836                                                                                                                                                                                                                                                                                                          
|Goodwill Allocated to Assets Sold                                                           | (61                                                                                                                                                                                                                                                                                                           
|Asset Retirement Obligations Associated with Assets Sold                                    | 20                                                                                                                                                                                                                                                                                                            
|Other Closing Adjustments                                                                   | (13                                                                                                                                                                                                                                                                                                           
|Gain on Divestitures                                                                        | $                                                                                                                                                                                                                                                                                                             
|Purchase Price Allocation of Acquisition                                                    | As a result of the transaction, we recorded the following:December 31, 2012(millions)Unproved Oil and Gas Properties$803Proved Oil and Gas Properties386Investment in CONE Gathering LLC69Total Assets Acquired(1)$1,258(1)Total reflects impact of$17 millionimputed interest on CONSOL installment payments.
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|                                                                                            |                                                                                                                                                                                                                                                                                                               
|                                                                                            | December 31, 2012                                                                                                                                                                                                                                                                                             
|(millions)                                                                                  |                                                                                                                                                                                                                                                                                                               
|Unproved Oil and Gas Properties                                                             | $                                                                                                                                                                                                                                                                                                             
|Proved Oil and Gas Properties                                                               | 386                                                                                                                                                                                                                                                                                                           
|Investment in CONE Gathering LLC                                                            | 69                                                                                                                                                                                                                                                                                                            
|Total Assets Acquired(1)                                                                    | $                                                                                                                                                                                                                                                                                                             
|                                                                                            |                                                                                                                                                                                                                                                                                                               
|(1)                                                                                         | Total reflects impact of$17 millionimputed interest on CONSOL installment payments.                                                                                                                                                                                                                           
|Schedule of Purchase Price Allocation - DJ Basin [Table Text Block]                         | The total purchase price and allocation of the total purchase price are as follows:December 31,2010(millions)Total Purchase PriceCash Paid$458Net Liabilities Assumed40Total$498Allocation of Total Purchase PriceProved Oil and Gas Properties$352Unproved Oil and Gas Properties146Total$498                
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|                                                                                            |                                                                                                                                                                                                                                                                                                               
|                                                                                            | December 31,                                                                                                                                                                                                                                                                                                  
|                                                                                            | 2010                                                                                                                                                                                                                                                                                                          
|(millions)                                                                                  |                                                                                                                                                                                                                                                                                                               
|Total Purchase Price                                                                        |                                                                                                                                                                                                                                                                                                               
|Cash Paid                                                                                   | $                                                                                                                                                                                                                                                                                                             
|Net Liabilities Assumed                                                                     | 40                                                                                                                                                                                                                                                                                                            
|Total                                                                                       | $                                                                                                                                                                                                                                                                                                             
|                                                                                            |                                                                                                                                                                                                                                                                                                               
|Allocation of Total Purchase Price                                                          |                                                                                                                                                                                                                                                                                                               
|Proved Oil and Gas Properties                                                               | $                                                                                                                                                                                                                                                                                                             
|Unproved Oil and Gas Properties                                                             | 146                                                                                                                                                                                                                                                                                                           
|Total                                                                                       | $                                                                                                                                                                                                                                                                                                             
|Schedule of Disposal Groups, Gain on Asset Sale Mid-Con & Illinois Basin [Table Text Block] | Information regarding the assets sold is as follows:Year Ended December 31,2010(millions)Cash Proceeds$552LessNet Book Value of Assets Sold(394)Goodwill Allocated to Assets Sold(61)Asset Retirement Obligations Associated with Assets Sold10Other Closing Adjustments3Gain on Asset Sale$110               
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|                                                                                            |                                                                                                                                                                                                                                                                                                               
|                                                                                            | Year Ended December 31,                                                                                                                                                                                                                                                                                       
|                                                                                            | 2010                                                                                                                                                                                                                                                                                                          
|(millions)                                                                                  |                                                                                                                                                                                                                                                                                                               
|Cash Proceeds                                                                               | $                                                                                                                                                                                                                                                                                                             
|Less                                                                                        |                                                                                                                                                                                                                                                                                                               
|Net Book Value of Assets Sold                                                               | (394                                                                                                                                                                                                                                                                                                          
|Goodwill Allocated to Assets Sold                                                           | (61                                                                                                                                                                                                                                                                                                           
|Asset Retirement Obligations Associated with Assets Sold                                    | 10                                                                                                                                                                                                                                                                                                            
|Other Closing Adjustments                                                                   | 3                                                                                                                                                                                                                                                                                                             
|Gain on Asset Sale                                                                          | $                                                                                                                                                                                                                                                                                                             

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