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Operating segments - Summary of depreciation and amortisation within the reportable segments (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated $ 4,375 $ 4,794 $ 4,645
Reportable segments [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 4,980 5,269 5,039
Reportable segments [Member] | Iron Ore [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 1,645 1,645 1,744
Reportable segments [Member] | Aluminium [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 1,199 1,250 1,172
Reportable segments [Member] | Copper & Diamonds [member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 1,452 1,601 1,261
Reportable segments [Member] | Energy & Minerals [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 652 739 830
Reportable segments [Member] | Other operations [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 32 34 32
Other items [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated 42 51 68
Depreciation and amortisation of equity accounted units [Member]      
Disclosure of operating segments [Line Items]      
Depreciation and amortisation expense proportionately consolidated $ (647) $ (526) $ (462)