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Capitalized Exploratory Well Costs - Changes In Capitalized Well Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Changes in Capitalized Well Costs      
Beginning balance $ 7 $ 36 $ 36
Additions pending the determination of proved reserves 0 7 74
Divestitures and other 0 (3) 0
Reclassifications to proved properties 0 (17) (40)
Charges to exploration expense (7) (16) (34)
Ending balance $ 0 $ 7 $ 36