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Capitalized Exploratory Well Costs (Tables)
 6 Months Ended
Jun. 30, 2019
Extractive Industries [Abstract]  
Summary of changes in capitalized well costs
A summary of the changes in our capitalized well costs for the Current Period is detailed below. Additions pending the determination of proved reserves excludes amounts capitalized and subsequently charged to expense within the same year.
 
 
2019
 
 
($ in millions)
Balance as of January 1
 
$
36

Additions pending the determination of proved reserves
 
9

Divestitures and other
 
—

Reclassifications to proved properties
 
(18
)
Charges to exploration expense
 
—

Balance as of June 30
 
$
27