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Directors' and key management remuneration - Additional information (Detail)
 12 Months Ended
Dec. 31, 2018
USD ($)
Director
Dec. 31, 2017
USD ($)
Director
Dec. 31, 2016
USD ($)
Director
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 39,592,000 $ 31,543,000 $ 44,218,000
Aggregate pension contribution to defined contribution plans 629,000 415,000 3,461,000
Other employment costs $ 2,360,000 $ 2,122,000 $ 2,295,000
Defined Benefit Plan      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Number of directors accrued retirement benefits under defined contribution arrangements | Director 0   1
Defined Contribution Plans      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Number of directors accrued retirement benefits under defined contribution arrangements | Director 3 2 2
Rio Tinto plc [member]      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 11,465,000 $ 12,624,000 $ 10,630,000
Aggregate pension contribution to defined contribution plans 80,000 135,000 69,000
Rio Tinto Limited [member]      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate pension contribution to defined contribution plans 0 0 0
Aggregate remuneration including pension contributions and other retirement benefits $ 607,000 $ 535,000 $ 1,696,000