|**Derivative Instruments and Hedging Activities (Details) (USD $)In Millions, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                                                       | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                            
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Derivative Instruments and Hedging Activities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|AOCL amount, net of tax, to be reclassified to interest expense over the life of the debt                                                                                                                                                                                                                                                                                                                                                                                                                        | $ 25                                                                                                                                                                                                                                                                                                                                                                                                                      
|Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months                                                                                                                                                                                                                                                                                                                                                                                                                                              | $ 2                                                                                                                                                                                                                                                                                                                                                                                                                       
|Crude Oil Commodity Contract | Swaps - NYMEX WTI 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI  (1)                                                                                                                                                                                                                                                                                                                                                                                                            
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 9,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 90.16                                                                                                                                                                                                                                                                                                                                                                                                                     
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Swaps - Dated Brent 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 3,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 98.03                                                                                                                                                                                                                                                                                                                                                                                                                     
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Two Way Collar - NYMEX WTI 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 95.00                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 115.00                                                                                                                                                                                                                                                                                                                                                                                                                    
|Crude Oil Commodity Contract | Three Way Collars - NYMEX WTI 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 7,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 63.57                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 83.57                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 109.04                                                                                                                                                                                                                                                                                                                                                                                                                    
|Crude Oil Commodity Contract | Three Way Collars - Dated Brent 2013                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 13,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 81.15                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 100.75                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 124.68                                                                                                                                                                                                                                                                                                                                                                                                                    
|Crude Oil Commodity Contract | Put Option - NYMEX WTI 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 11,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 5.97                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 97.60                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Swaps - NYMEX WTI 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 37,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 92.67                                                                                                                                                                                                                                                                                                                                                                                                                     
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Swaps - Dated Brent 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 10,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 103.33                                                                                                                                                                                                                                                                                                                                                                                                                    
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Three Way Collars - NYMEX WTI 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 9,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 75.89                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 90.89                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 100.44                                                                                                                                                                                                                                                                                                                                                                                                                    
|Crude Oil Commodity Contract | Three Way Collars - Dated Brent 2014                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 8,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 84.38                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 98.25                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 121.56                                                                                                                                                                                                                                                                                                                                                                                                                    
|Crude Oil Commodity Contract | Swaps - NYMEX WTI 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 10,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 87.01                                                                                                                                                                                                                                                                                                                                                                                                                     
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Swaps - Dated Brent 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 99.04                                                                                                                                                                                                                                                                                                                                                                                                                     
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Crude Oil Commodity Contract | Three Way Collars - NYMEX WTI 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX WTI                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 10,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 68.50                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 88.50                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 92.87                                                                                                                                                                                                                                                                                                                                                                                                                     
|Crude Oil Commodity Contract | Three Way Collars - Dated Brent 2015                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Dated Brent                                                                                                                                                                                                                                                                                                                                                                                                               
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5,000                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Put Option Premium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 75.00                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 95.00                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 112.53                                                                                                                                                                                                                                                                                                                                                                                                                    
|Natural Gas Commodity Contract | Swaps - NYMEX HH 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH (1)                                                                                                                                                                                                                                                                                                                                                                                                              
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 60,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 4.58                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Natural Gas Commodity Contract | Two Way Collar - NYMEX HH 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 40,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 3.25                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5.14                                                                                                                                                                                                                                                                                                                                                                                                                      
|Natural Gas Commodity Contract | Three Way Collars - NYMEX HH 2013                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2013                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 100,000                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 3.88                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 4.75                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5.63                                                                                                                                                                                                                                                                                                                                                                                                                      
|Natural Gas Commodity Contract | Swaps - NYMEX HH 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 60,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 4.24                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Natural Gas Commodity Contract | Three Way Collar - NYMEX HH 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2014                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 230,000                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 2.83                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 3.75                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 4.98                                                                                                                                                                                                                                                                                                                                                                                                                      
|Natural Gas Commodity Contract | Swaps - NYMEX HH 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 80,000                                                                                                                                                                                                                                                                                                                                                                                                                    
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 4.32                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Natural Gas Commodity Contract | Three Way Collars - NYMEX HH 2015                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                           
|**Derivative [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 2015                                                                                                                                                                                                                                                                                                                                                                                                                      
|Index                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | NYMEX HH                                                                                                                                                                                                                                                                                                                                                                                                                  
|Volume Per Day                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 120,000                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted Average Fixed Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                           
|Weighted Average Short Put Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 3.54                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Floor Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 4.25                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted Average Ceiling Price                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 5.06                                                                                                                                                                                                                                                                                                                                                                                                                      
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|[1]
              West Texas Intermediate[2]
              For put options, we typically pay a premium to the counterparty in exchange for the sale of the instrument. If the index price is below the floor price of the put option, we receive the difference between the floor price and the index price multiplied by the contract volumes less the option premium. If the index price settles at or above the floor price of the put option, we pay only the put option premium.[3]
              Henry Hub | [1]                                                                                                                                                                                                                                                                                                                                                                                                                       
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | West Texas Intermediate                                                                                                                                                                                                                                                                                                                                                                                                   
|[2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | For put options, we typically pay a premium to the counterparty in exchange for the sale of the instrument. If the index price is below the floor price of the put option, we receive the difference between the floor price and the index price multiplied by the contract volumes less the option premium. If the index price settles at or above the floor price of the put option, we pay only the put option premium.
|[3]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | Henry Hub                                                                                                                                                                                                                                                                                                                                                                                                                 

X- DefinitionAggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B+ Details**Name:**
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                    instant X- DefinitionThe estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.+ Details**Name:**
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                    instant X- DefinitionReference to the index or unit of measurement for the underlying which establishes the pricing terms of the derivative instrument. For example, the basis on the underlying for a natural gas futures contract might be the NYMEX price per million British thermal units (MMBtu).+ ReferencesNo definition available.+ Details**Name:**
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