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Directors' and key management remuneration - Additional information (Detail)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
USD ($)
Director
Dec. 31, 2018
USD ($)
Director
Dec. 31, 2017
USD ($)
Director
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 40,494 $ 39,592 $ 31,543
Aggregate pension contribution to defined contribution plans 477 629 415
Other employment costs $ 2,066 $ 2,360 $ 2,122
Defined Benefit Plan      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Number of directors accrued retirement benefits under defined contribution arrangements | Director 0    
Defined Contribution Plans      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Number of directors accrued retirement benefits under defined contribution arrangements | Director 2 3 2
Rio Tinto plc [Member]      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 11,565 $ 11,465 $ 12,624
Aggregate pension contribution to defined contribution plans 42 80 135
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 $ 749 $ 607 $ 535