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Operating segments - Summary of capital expenditure within the reportable segments (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of operating segments [Line Items]      
Capital expenditure $ 5,439 $ 4,844 $ 4,344
Sales of property, plant and equipment and intangible assets 49 586 138
Capital expenditure per cash flow statement 5,488 5,430 4,482
Reportable segments [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 5,831 5,279 4,691
Reportable segments [Member] | Iron ore [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 1,741 1,302 1,214
Reportable segments [Member] | Aluminium [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 1,456 1,373 1,436
Reportable segments [Member] | Copper & Diamonds [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 2,087 2,150 1,622
Reportable segments [Member] | Energy & Minerals [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 551 442 454
Reportable segments [Member] | Other operations [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure (4) 12 (35)
Other items [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure 64 65 70
Capital expenditure of equity accounted units [Member]      
Disclosure of operating segments [Line Items]      
Capital expenditure $ (456) (500) $ (417)
Kitimat [Member]      
Disclosure of operating segments [Line Items]      
Sales of property, plant and equipment and intangible assets   $ 508