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Financial instruments and risk management - Summary of capital and liquidity risk management (Detail) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of detailed information about hedging instruments [Line Items]      
Equity attributable to owners of Rio Tinto (see Group balance sheet) $ 44,711 $ 39,290 $ 37,349
Equity attributable to non-controlling interests (see Group balance sheet) 6,404 6,440  
Net debt 3,845 9,587 $ 13,783
Capital and liquidity risk management [member]      
Disclosure of detailed information about hedging instruments [Line Items]      
Equity attributable to owners of Rio Tinto (see Group balance sheet) 44,711 39,290  
Equity attributable to non-controlling interests (see Group balance sheet) 6,404 6,440  
Net debt 3,845 9,587  
Total capital $ 54,960 $ 55,317