Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Oil and Gas Reserves) (Details)

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Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Oil and Gas Reserves) (Details)
 12 Months Ended
Dec. 31, 2015
MMcf
MBbls
Dec. 31, 2015
MMcf
MBbls
Dec. 31, 2014
MMcf
MBbls
Dec. 31, 2014
MMcf
MBbls
Dec. 31, 2013
MMcf
MBbls
Dec. 31, 2013
MMcf
MBbls
Oil and condensate sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period   9,497   8,346   8,106
Purchases in oil and gas reserves in place   0   173   0
Extensions and discoveries   2,413   4,975   2,765
Revisions of prior reserve estimates   (2,553)   (1,313)   (208)
Current production   (2,899)   (2,684)   (2,317)
End of period   6,458   9,497   8,346
Proved developed reserves 6,120 6,120 5,719 5,719 5,609 5,609
Proved undeveloped reserves 338 338 3,778 3,778 2,737 2,737
Natural gas liquids sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period 719,006 719,006 146,446 146,446 33,771  
Purchases in oil and gas reserves in place | MMcf 371,663   8,863   0  
Extensions and discoveries | MMcf 997,057   629,151   123,597  
Revisions of prior reserve estimates | MMcf (371,430)   (6,136)   (2,031)  
Current production | MMcf (156,151)   (59,318)   (8,891)  
End of period   1,560,145 719,006 719,006 146,446 146,446
Proved developed reserves | MMcf 652,961 652,961 345,166 345,166 94,552 94,552
Proved undeveloped reserves | MMcf 907,184 907,184 373,840 373,840 51,894 51,894
Natural Gas Liquids            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period   26,268   5,675   145
Purchases in oil and gas reserves in place   0   353   0
Extensions and discoveries   5,486   22,594   5,850
Revisions of prior reserve estimates   (9,594)   (304)   0
Current production   (4,424)   (2,050)   (320)
End of period   17,736   26,268   5,675
Proved developed reserves 12,910 12,910 12,379 12,379 3,527 3,527
Proved undeveloped reserves 4,826 4,826 13,889 13,889 2,148 2,148
Diamondback Energy, Inc | Oil and condensate sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period       3,067   5,606
Change in ownership interest in Diamondback           (3,720)
Purchases in oil and gas reserves in place           528
Extensions and discoveries           1,227
Revisions of prior reserve estimates           (428)
Current production           (146)
End of period           3,067
Proved developed reserves         1,425 1,425
Proved undeveloped reserves         1,642 1,642
Diamondback Energy, Inc | Natural gas liquids sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period | MMcf     4,441   7,398  
Change in ownership interest in Diamondback | MMcf         (4,909)  
Purchases in oil and gas reserves in place | MMcf         752  
Extensions and discoveries | MMcf         1,741  
Revisions of prior reserve estimates | MMcf         (417)  
Current production | MMcf         (124)  
End of period | MMcf         4,441  
Proved developed reserves | MMcf         2,263 2,263
Proved undeveloped reserves | MMcf         2,178 2,178
Diamondback Energy, Inc | Natural Gas Liquids            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period       771   1,766
Change in ownership interest in Diamondback           (1,171)
Purchases in oil and gas reserves in place           120
Extensions and discoveries           331
Revisions of prior reserve estimates           (249)
Current production           (26)
End of period           771
Proved developed reserves         358 358
Proved undeveloped reserves         413 413
Investment in Grizzly Oil Sands ULC | Oil and condensate sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period   14,558,000   13,637,000    
Purchases in oil and gas reserves in place   0   0    
Extensions and discoveries   0   0    
Revisions of prior reserve estimates   (14,530,000)   990,000    
Current production   (28,000)   (69,000)    
End of period   0   14,558,000   13,637,000
Proved developed reserves 0 0 2,000 2,000    
Proved undeveloped reserves 0 0 13,000 13,000    
Investment in Grizzly Oil Sands ULC | Natural gas liquids sales            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period | MMcf 0   0      
Purchases in oil and gas reserves in place | MMcf 0   0      
Extensions and discoveries | MMcf 0   0      
Revisions of prior reserve estimates | MMcf 0   0      
Current production | MMcf 0   0      
End of period | MMcf 0   0   0  
Proved developed reserves | MMcf 0 0 0 0    
Proved undeveloped reserves | MMcf 0 0 0 0    
Investment in Grizzly Oil Sands ULC | Natural Gas Liquids            
Proved Developed and Undeveloped Reserves [Roll Forward]            
Beginning of the period   0   0    
Purchases in oil and gas reserves in place   0   0    
Extensions and discoveries   0   0    
Revisions of prior reserve estimates   0   0    
Current production   0   0    
End of period   0   0   0
Proved developed reserves 0 0 0 0    
Proved undeveloped reserves 0 0 0 0