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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Beginning asset retirement obligations $ 183 $ 271  
New wells placed on production 5 1  
Changes in estimates (a) 82 16  
Dispositions (37) (89)  
Liabilities settled (52) (30)  
Accretion of discount 10 14 $ 19
Ending asset retirement obligations 191 183 $ 271
Asset retirement obligations, current portion 73 25  
Asset retirement obligations, long term $ 118 $ 158