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Share capital - Rio Tinto plc - Additional information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
American depository receipts      
Disclosure of classes of share capital [line items]      
Value of shares purchased by employee share ownership trusts $ 31 $ 43 $ 140
Rio Tinto plc      
Disclosure of classes of share capital [line items]      
Shares held in the employee share ownership trusts on behalf of Rio Tinto plc 273,902    
Rio Tinto plc | American depository receipts      
Disclosure of classes of share capital [line items]      
American Depository Reciepts In Entity Held In Employee Share Ownership Trust 41,240