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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Beginning asset retirement obligations $ 191 $ 183  
New wells placed on production 5 5  
Changes in estimates (a) 109 82  
Dispositions 0 (37)  
Liabilities settled (32) (52)  
Accretion of discount 9 10 $ 14
Asset retirement obligations, long-term 282 191 $ 183
Asset Retirement Obligations, Noncurrent 240 118  
Asset retirement obligations, current portion $ 42 $ 73