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Accounts receivable (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accounts receivable      
Accounts receivable $ 4,993 $ 2,529  
Impairment of accounts receivable recorded in the income statement $ 5 $ (1) $ (7)
Steel industry market      
Accounts receivable      
Perecentage of revenue 87.25% 87.33%  
One Customer | Ferrous minerals      
Accounts receivable      
Perecentage of revenue 10.10%    
Accounts receivable      
Accounts receivable      
Expected credit loss $ (50) $ (63)  
Carrying amount      
Accounts receivable      
Accounts receivable $ 5,043 $ 2,592