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Accounting for Suspended Exploratory Wells - Narrative (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Project
Well
Dec. 31, 2019
USD ($)
Project
Dec. 31, 2018
USD ($)
Project
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for period greater than one year | $ $ 2,486 $ 2,827 $ 3,361
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project 17 22 30
Expected period for decision on the recognition of proved reserves 5 years    
Capitalized exploratory well costs that have been capitalized for period greater than one year, number of wells | Well 89    
Drilling Activity      
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for period greater than one year | $ $ 1,197    
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project 7    
No Drilling Activity      
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for period greater than one year | $ $ 1,289    
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project 10    
Undergoing Front End Engineering and Design with Final Investment Decision Expected      
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for period greater than one year | $ $ 826    
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project 7    
Undergoing front-end engineering and design with final investment decision expected in three years 4 years    
Reviewing Development Alternatives      
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for period greater than one year | $ $ 463    
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project 3