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Other reserves - Additional information (Detail) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Disclosure Of Reserves Within Equity [Line Items]    
Other reserves $ 12,284 $ 9,216
Rio Tinto plc [member]    
Disclosure Of Reserves Within Equity [Line Items]    
Other reserves 11,992 11,988
Merger reserve [Member]    
Disclosure Of Reserves Within Equity [Line Items]    
Other reserves 11,936  
Merger reserve [Member] | Rio Tinto plc [member]    
Disclosure Of Reserves Within Equity [Line Items]    
Other reserves $ 11,936 $ 11,936