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Financial instruments and risk management - Summary of capital and liquidity risk management (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about hedging instruments [Line Items]        
Equity attributable to owners of Rio Tinto (see Group balance sheet) $ 43,686 $ 44,542 $ 44,711 $ 39,290
Equity attributable to non-controlling interests (see Group balance sheet) 6,137   6,404  
Net debt (255)   3,845 $ 9,587
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) 43,686   44,711  
Equity attributable to non-controlling interests (see Group balance sheet) 6,137   6,404  
Net debt (255)   3,845  
Total capital $ 49,568   $ 54,960