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Share-based payments - Summary of options outstanding and exercisable (Detail)
$ in Millions
Dec. 31, 2018
USD ($)
Option
Dec. 31, 2018
GBP (£)
Option
Dec. 31, 2017
Option
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number 40,114 40,114 188,766
Aggregate intrinsic value | $ $ 1    
Rio Tinto plc [member] | Exercise price GBPXX - GBPXX [member] | Share Option Plan [member]      
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number 23,659 23,659  
Weighted average exercise price per option | £   £ 17  
Weighted average remaining contractual life Years 0.22 0.22  
Aggregate intrinsic value | $ $ 1    
Rio Tinto Limited [member] | Exercise price A$XX [member] | Share Option Plan [member]      
Disclosure Of Terms And Conditions Of Sharebased Payment Arrangement [Line Items]      
Options outstanding, number 16,455 16,455  
Weighted average exercise price per option | £   £ 33  
Weighted average remaining contractual life Years 0.21 0.21