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Share-based payments - Summary of options outstanding and exercisable (Detail)
$ in Millions
Dec. 31, 2017
USD ($)
Option
Dec. 31, 2017
GBP (£)
Option
Dec. 31, 2016
Option
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number | Option 188,766 188,766 567,598
Aggregate intrinsic value | $ $ 3    
Rio Tinto plc [member] | Exercise price GBP16 - GBP43 [member] | Share Option Plan [member]      
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number | Option 164,119 164,119  
Weighted average exercise price per option | £   £ 32  
Weighted average remaining contractual life Years 2.56 2.56  
Aggregate intrinsic value | $ $ 2    
Rio Tinto Limited [member] | Exercise price A$33 [member] | Share Option Plan [member]      
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number | Option 24,647 24,647  
Weighted average exercise price per option | £   £ 33  
Weighted average remaining contractual life Years 1.21 1.21  
Aggregate intrinsic value | $ $ 1