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SUPPLEMENTARY OIL & GAS INFORMATION (Unaudited) - Proved and Proved Developed Natural Gas Reserve Quantities (Details) - Natural Gas
 12 Months Ended
Dec. 31, 2019
MMBbls
Bcf
Dec. 31, 2018
MMBbls
Bcf
Dec. 31, 2017
MMBbls
Bcf
Dec. 31, 2016
Bcf
Proved Developed And Undeveloped Reserves [Roll Forward]        
Proved reserves, net, beginning balance 4,354 5,240 4,644  
Extensions and discoveries (in Bcf) 106 90 261  
Improved recovery (in Bcf) 202 414 179  
Purchases of reserves in place (in Bcf) 34 67 106  
Sales of reserves in place (in Bcf) 0 (3) 0  
Production (in Bcf) (528) (542) (579)  
Economic revisions due to prices (in Bcf) 248 (748) 407  
Revisions of prior estimates (in Bcf) 367 (164) 222  
Proved reserves, net, ending balance 4,782 4,354 5,240  
Net proved developed reserves (in Bcf) 2,381 2,417 3,112 2,841
Change in proved developed and undeveloped reserves, net (in Bcf) | MMBbls 428 886 596  
North America        
Proved Developed And Undeveloped Reserves [Roll Forward]        
Proved reserves, net, beginning balance 4,306 5,199 4,594  
Extensions and discoveries (in Bcf) 106 90 261  
Improved recovery (in Bcf) 202 414 179  
Purchases of reserves in place (in Bcf) 34 67 106  
Sales of reserves in place (in Bcf) 0 (3) 0  
Production (in Bcf) (511) (523) (558)  
Economic revisions due to prices (in Bcf) 246 (746) 403  
Revisions of prior estimates (in Bcf) 346 (192) 214  
Proved reserves, net, ending balance 4,728 4,306 5,199  
Net proved developed reserves (in Bcf) 2,342 2,382 3,081 2,805
North Sea        
Proved Developed And Undeveloped Reserves [Roll Forward]        
Proved reserves, net, beginning balance 27 25 25  
Extensions and discoveries (in Bcf) 0 0 0  
Improved recovery (in Bcf) 0 0 0  
Purchases of reserves in place (in Bcf) 0 0 0  
Sales of reserves in place (in Bcf) 0 0 0  
Production (in Bcf) (9) (11) (14)  
Economic revisions due to prices (in Bcf) 0 0 5  
Revisions of prior estimates (in Bcf) (2) 13 9  
Proved reserves, net, ending balance 16 27 25  
Net proved developed reserves (in Bcf) 11 23 22 18
Offshore Africa        
Proved Developed And Undeveloped Reserves [Roll Forward]        
Proved reserves, net, beginning balance 21 16 25  
Extensions and discoveries (in Bcf) 0 0 0  
Improved recovery (in Bcf) 0 0 0  
Purchases of reserves in place (in Bcf) 0 0 0  
Sales of reserves in place (in Bcf) 0 0 0  
Production (in Bcf) (8) (8) (7)  
Economic revisions due to prices (in Bcf) 2 (2) (1)  
Revisions of prior estimates (in Bcf) 23 15 (1)  
Proved reserves, net, ending balance 38 21 16  
Net proved developed reserves (in Bcf) 28 12 9 18