|**Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) (USD $)In Millions, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | Sep. 30, 2012                                                                                                                                                                                                                                                          | Dec. 31, 2011                                                                                                                                                                                                                                                         
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | $ 110                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 59                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                       
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | (21)                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                       
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | (169)                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                       
|Quoted Prices in Active Markets (Level 1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 110                                                                                                                                                                                                                                                                    | [1]                                                                                                                                                                                                                                                                   
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0                                                                                                                                                                                                                                                                      | [1]                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0                                                                                                                                                                                                                                                                      | [1]                                                                                                                                                                                                                                                                   
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | (169)                                                                                                                                                                                                                                                                  | [1]                                                                                                                                                                                                                                                                   
|Significant Other Observable Inputs (Level 2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0                                                                                                                                                                                                                                                                      | [2]                                                                                                                                                                                                                                                                   
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 102                                                                                                                                                                                                                                                                    | [2]                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | (64)                                                                                                                                                                                                                                                                   | [2]                                                                                                                                                                                                                                                                   
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 0                                                                                                                                                                                                                                                                      | [2]                                                                                                                                                                                                                                                                   
|Significant Unobservable Inputs (Level 3)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0                                                                                                                                                                                                                                                                      | [3]                                                                                                                                                                                                                                                                   
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0                                                                                                                                                                                                                                                                      | [3]                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0                                                                                                                                                                                                                                                                      | [3]                                                                                                                                                                                                                                                                   
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 0                                                                                                                                                                                                                                                                      | [3]                                                                                                                                                                                                                                                                   
|Fair Value Inputs Adjustment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0                                                                                                                                                                                                                                                                      | [4]                                                                                                                                                                                                                                                                   
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | (43)                                                                                                                                                                                                                                                                   | [4]                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 43                                                                                                                                                                                                                                                                     | [4]                                                                                                                                                                                                                                                                   
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | $ 0                                                                                                                                                                                                                                                                    | [4]                                                                                                                                                                                                                                                                   
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|[1]
              Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.[2]
              Level 2 measurements are fair value measurements which use inputs, other than quoted prices included within Level 1, which are observable for the asset or liability, either directly or indirectly.[3]
              Level 3 measurements are fair value measurements which use unobservable inputs.[4]
              Amount represents the impact of master netting agreements that allow us to net cash settle asset and liability positions with the same counterparty. | [1]                                                                                                                                                                                                                                                                    | Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.
|[2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Level 2 measurements are fair value measurements which use inputs, other than quoted prices included within Level 1, which are observable for the asset or liability, either directly or indirectly.                                                                  
|[3]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Level 3 measurements are fair value measurements which use unobservable inputs.                                                                                                                                                                                       
|[4]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Amount represents the impact of master netting agreements that allow us to net cash settle asset and liability positions with the same counterparty.                                                                                                                  

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