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Intangible assets - Exploration expenditures (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets $ 2,260 $ 3,014  
Exploration expenditures 1,371 1,584 $ 1,438
Expensed exploration expenditures previously capitalised 2,506 777 357
Capitalised exploration (394) (507) (390)
Exploration expenses 3,483 1,854 $ 1,405
Less than one year [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets 604 684  
Between one and five years [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets 623 1,056  
More than five years [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets $ 1,033 $ 1,274