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Directors' and key management remuneration - Additional information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Director
Dec. 31, 2016
USD ($)
Director
Dec. 31, 2015
USD ($)
Director
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 31,543,000 $ 44,218,000 $ 44,231,000
Aggregate pension contribution to defined contribution plans 415,000 3,461,000 1,049,000
Other employment costs $ 2,122,000 $ 2,295,000 $ 2,320,000
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 1
Defined Contribution Plans      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Number of directors accrued retirement benefits under defined contribution arrangements | Director 2 2 1
Rio Tinto plc [member]      
Disclosure Of Directors And Key Management Remuneration [Line Items]      
Aggregate remuneration incurred $ 12,624,000 $ 10,630,000 $ 6,385,000
Aggregate pension contribution to defined contribution plans 135,000 69,000 52,000
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 $ 535,000 $ 1,696,000 $ 6,375,000