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Operating segments - Additional information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of operating segments [Line Items]      
Percentage of capital expenditure 100.00%    
Percentage of depreciation and amortisation 100.00%    
Share of profit after tax of equity accounted units $ 301 $ 513 $ 339
Subsidiaries [Member]      
Disclosure of operating segments [Line Items]      
Share of sales revenue of equity accounted units 32 41 22
Gross sales revenue [Member]      
Disclosure of operating segments [Line Items]      
Share of sales revenue of equity accounted units 2,234 2,354 1,859
Underlying earnings [Member]      
Disclosure of operating segments [Line Items]      
Share of profit after tax of equity accounted units 302 513 332
Underlying earnings [Member] | Copper & Diamonds [Member]      
Disclosure of operating segments [Line Items]      
Share of profit after tax of equity accounted units 292 476 295
Underlying earnings [Member] | Other operations [Member]      
Disclosure of operating segments [Line Items]      
Share of profit after tax of equity accounted units $ 10 $ 37 $ 37