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Intangible assets - Exploration expenditures (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets $ 3,014 $ 2,685  
Exploration expenditures 1,584 1,438 $ 1,234
Expensed exploration expenditures previously capitalised 777 357 (8)
Capitalised exploration (507) (390) (167)
Exploration expenses 1,854 1,405 $ 1,059
2019 [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets 1,274 392  
Between one and five years [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets 1,056 1,406  
More than five years [member]      
Disclosure of detailed information about intangible assets [line items]      
Intangible exploration and evaluation assets $ 684 $ 887