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Share-based payments - Summary of performance share plans (Detail) - Performance share plans [member]
 12 Months Ended
Dec. 31, 2019
shares
£ / shares
Dec. 31, 2019
shares
$ / shares
Dec. 31, 2018
shares
£ / shares
Dec. 31, 2018
shares
$ / shares
Rio Tinto plc [Member]        
Disclosure of terms and conditions of share-based payment arrangement [line items]        
Number of non-vested shares at beginning balance 3,845,082 3,845,082 3,555,274 3,555,274
Number of non-vested shares, awarded 755,735 755,735 801,047 801,047
Number of non-vested shares, forfeited (122,961) (122,961) (188,761) (188,761)
Number of non-vested shares, failed performance conditions (384,130) (384,130) (107,625) (107,625)
Number of non-vested shares, vested (290,332) (290,332) (214,853) (214,853)
Number of non-vested shares at ending balance 3,803,394 3,803,394 3,845,082 3,845,082
Weighted average fair value at grant date, non-vested shares at beginning balance | £ / shares £ 21.86   £ 20.47  
Weighted average fair value at grant date, non-vested shares, awarded | £ / shares 24.68   26.87  
Weighted average fair value at grant date, non-vested shares, forfeited | £ / shares 23.95   21.45  
Weighted average fair value at grant date, non-vested shares, failed performance conditions | £ / shares 23.79   14.54  
Weighted average fair value at grant date, non-vested shares, vested | £ / shares 21.36   21.57  
Weighted average fair value at grant date, non-vested shares ending balance | £ / shares £ 22.20   £ 21.86  
Number of vested awards settled in shares during the year (including dividend shares applied on vesting) 339,821 339,821 248,965 248,965
Number of vested awards settled in cash during the year (including dividend shares applied on vesting) 1,279 1,279 991 991
Weighted average share price, Vested awards settled in shares during the year (including dividend shares applied on vesting) | £ / shares £ 45.52   £ 42.57  
Rio Tinto Limited [Member]        
Disclosure of terms and conditions of share-based payment arrangement [line items]        
Number of non-vested shares at beginning balance 1,797,279 1,797,279 1,609,154 1,609,154
Number of non-vested shares, awarded 297,189 297,189 387,298 387,298
Number of non-vested shares, forfeited (126,775) (126,775) (36,530) (36,530)
Number of non-vested shares, failed performance conditions (188,956) (188,956) (54,322) (54,322)
Number of non-vested shares, vested (142,220) (142,220) (108,321) (108,321)
Number of non-vested shares at ending balance 1,636,517 1,636,517 1,797,279 1,797,279
Weighted average fair value at grant date, non-vested shares at beginning balance | $ / shares   $ 43.34   $ 40.13
Weighted average fair value at grant date, non-vested shares, awarded | $ / shares   54.55   53.85
Weighted average fair value at grant date, non-vested shares, forfeited | $ / shares   44.02   43.83
Weighted average fair value at grant date, non-vested shares, failed performance conditions | $ / shares   46.42   27.67
Weighted average fair value at grant date, non-vested shares, vested | $ / shares   41.72   40.85
Weighted average fair value at grant date, non-vested shares ending balance | $ / shares   $ 45.11   $ 43.34
Number of vested awards settled in shares during the year (including dividend shares applied on vesting) 151,607 151,607 105,374 105,374
Number of vested awards settled in cash during the year (including dividend shares applied on vesting) 1,347 1,347 9,959 9,959
Weighted average share price, Vested awards settled in shares during the year (including dividend shares applied on vesting) | $ / shares   $ 100.30   $ 82.97
Weighted average share price, Vested awards settled in cash during the year (including dividend shares applied on vesting) | (per share) £ 43.65 $ 92.97 £ 42.40 $ 82.08