|**Property Transactions (Tables)**                             | 12 Months Ended                                                                                                                                                                                                                                                                                                                
|-------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Discontinued Operations and Disposal Groups [Abstract]**     |                                                                                                                                                                                                                                                                                                                                
|Summary of Discontinued Operations                             | Summarized results of discontinued operations are as follows:Year Ended December 31,(millions)201320122011Oil and Gas Sales$37$208$357Income Before Income Taxes12101215Income Tax Expense655174Operating Income, Net of Tax64641Gain on Sale, Net of Tax6516—Discontinued Operations, Net of Tax$71$62$41                     
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|                                                               |                                                                                                                                                                                                                                                                                                                                
|                                                               | Year Ended December 31,                                                                                                                                                                                                                                                                                                        
|(millions)                                                     | 2013                                                                                                                                                                                                                                                                                                                           
|Oil and Gas Sales                                              | $                                                                                                                                                                                                                                                                                                                              
|Income Before Income Taxes                                     | 12                                                                                                                                                                                                                                                                                                                             
|Income Tax Expense                                             | 6                                                                                                                                                                                                                                                                                                                              
|Operating Income, Net of Tax                                   | 6                                                                                                                                                                                                                                                                                                                              
|Gain on Sale, Net of Tax                                       | 65                                                                                                                                                                                                                                                                                                                             
|Discontinued Operations, Net of Tax                            | $                                                                                                                                                                                                                                                                                                                              
|Schedule of Disposal Groups, Gain on Divestitures - Onshore US | The information regarding the assets sold is as follows:Year Ended December 31,(millions)20132012Cash Proceeds$150$1,044LessNet Book Value of Assets Sold(117)(836)Goodwill Allocated to Assets Sold(8)(61)Asset Retirement Obligations Associated with Assets Sold820Other Closing Adjustments3(13)Gain on Divestitures$36$154
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|                                                               |                                                                                                                                                                                                                                                                                                                                
|                                                               |                                                                                                                                                                                                                                                                                                                                
|(millions)                                                     |                                                                                                                                                                                                                                                                                                                                
|Cash Proceeds                                                  |                                                                                                                                                                                                                                                                                                                                
|Less                                                           |                                                                                                                                                                                                                                                                                                                                
|Net Book Value of Assets Sold                                  |                                                                                                                                                                                                                                                                                                                                
|Goodwill Allocated to Assets Sold                              |                                                                                                                                                                                                                                                                                                                                
|Asset Retirement Obligations Associated with Assets Sold       |                                                                                                                                                                                                                                                                                                                                
|Other Closing Adjustments                                      |                                                                                                                                                                                                                                                                                                                                
|Gain on Divestitures                                           |                                                                                                                                                                                                                                                                                                                                
|Purchase Price Allocation of Acquisition                       | the following:(millions)December 31, 2012Unproved 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.                                                             
|                                                              
|                                                               |                                                                                                                                                                                                                                                                                                                                
|(millions)                                                     | December 31, 2012                                                                                                                                                                                                                                                                                                              
|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.                                                                                                                                                                                                                                            

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