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Suspended Exploratory Well Costs (Tables)
 12 Months Ended
Dec. 31, 2017
SUSPENDED EXPLORATORY WELL COSTS  
Schedule of capitalized well cost rollforward

                                                                                                                                                                                    

($ millions)

 
2017

 
2016

 

 

Beginning of year

 

—

 
212

 

 

Additions

 

—

 
209

 

 

Transfers to oil and gas assets

 

—

 
(65

)

 

Capitalized exploratory well costs charged to expense

 

—

 
(356

)

 

End of year

 

—

 

—