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Operating segments - Summary of gross sales revenue within the reportable segments (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of operating segments [Line Items]      
Consolidated sales revenue $ 40,522 $ 40,030 $ 33,781
Reportable segments [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 42,850 41,872 35,329
Reportable segments [Member] | Iron Ore [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 18,485 18,251 14,605
Reportable segments [Member] | Aluminium [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 12,191 11,005 9,458
Reportable segments [Member] | Copper & Diamonds [member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 6,468 4,842 4,524
Reportable segments [Member] | Energy & Minerals [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 5,697 7,764 6,734
Reportable segments [Member] | Other operations [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 9 10 8
Inter-segment transactions [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue (15) (15) (11)
Product group [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 42,835 41,857 35,318
Items excluded from underlying earnings [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue   10 18
Gross sales revenue [Member]      
Disclosure of operating segments [Line Items]      
Consolidated sales revenue 42,835 41,867 35,336
Share of equity accounted units and adjustments [Member]      
Disclosure of operating segments [Line Items]      
Sales revenue $ (2,313) $ (1,837) $ (1,555)