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Principal associates - Summary of principal associates (Detail) - shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of associates [Line Items]      
Rio Tinto Limited shares were held by Rio Tinto plc 0 0 0
Boyne Smelters Limited | Ordinary      
Disclosure of associates [Line Items]      
Company of operation, Associate Boyne Smelters Limited    
Rio Tinto Limited shares were held by Rio Tinto plc 153,679,560    
Proportion of class held (%), Associate 59.40%    
Group interest (%), Associate 59.40%    
Mineracao Rio do Norte S.A.      
Disclosure of associates [Line Items]      
Group interest (%), Associate 12.00%    
Mineracao Rio do Norte S.A. | Ordinary      
Disclosure of associates [Line Items]      
Rio Tinto Limited shares were held by Rio Tinto plc 25,000,000,000    
Proportion of class held (%), Associate 12.50%    
Mineracao Rio do Norte S.A. | Preferred Shares      
Disclosure of associates [Line Items]      
Company of operation, Associate Mineracao Rio do Norte S.A.    
Rio Tinto Limited shares were held by Rio Tinto plc 47,000,000,000    
Proportion of class held (%), Associate 11.75%    
Mineracao Rio do Norte S.A. | Common and preferred shares      
Disclosure of associates [Line Items]      
Group interest (%), Associate 12.00%    
Halco Mining Inc      
Disclosure of associates [Line Items]      
Group interest (%), Associate 51.00%    
Halco Mining Inc | Common      
Disclosure of associates [Line Items]      
Company of operation, Associate Halco (Mining) Inc    
Rio Tinto Limited shares were held by Rio Tinto plc 4,500    
Proportion of class held (%), Associate 45.00%    
Group interest (%), Associate 45.00%