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Share capital - Rio Tinto plc - Summary of share capital (Parenthetical) (Detail) - Rio Tinto plc [member]
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2017
USD ($)
£ / shares
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2016
USD ($)
£ / shares
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2015
USD ($)
£ / shares
shares
Dec. 31, 2014
USD ($)
Disclosure Of Classes Of Share Capital [Line Items]              
Ordinary shares issued 26,241 26,241 33,210 33,210 21,709 21,709  
Number of shares bought back 32,937,109   0   40,912,881    
Share capital | $ $ 220.0 $ 220.0 $ 224.0 $ 224.0 $ 224.0 $ 224.0 $ 230.0
Treasury stock reissued | $ $ 2.0   $ 4.0   $ 13.0    
Treasury shares [Member]              
Disclosure Of Classes Of Share Capital [Line Items]              
Ordinary shares issued 147,126 147,126 743,380 743,380      
Rio Tinto Plc employee share based payment plans [member]              
Disclosure Of Classes Of Share Capital [Line Items]              
Ordinary shares issued 0 0 0 0 0 0  
Exercise prices per share | £ / shares   $ 28.63   $ 16.53   $ 15.09  
Market value per share | £ / shares   $ 37.78   $ 32.23   $ 32.37  
Rio Tinto Plc employee share based payment plans [member] | Treasury shares [Member]              
Disclosure Of Classes Of Share Capital [Line Items]              
Shares reissued from treasury 147,126   743,380   789,887    
Global employee share plan [member]              
Disclosure Of Classes Of Share Capital [Line Items]              
Share capital | $ $ 1.0 $ 1.0 $ 0.9 $ 0.9 $ 0.9 $ 0.9