Contingencies and commitments - Additional information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure of commitments and contingencies [Line Items]
Contractual capital commitments	$ 1,500.0	$ 900.0
Borrowings	$ 13,831.0	14,115.0
Turquoise Hill Resources Ltd(including Oyu Tolgoi LLC)
Disclosure of commitments and contingencies [Line Items]
Group interest (%)	50.80%
Oyu Tolgoi
Disclosure of commitments and contingencies [Line Items]
Borrowings	$ 4,300.0	4,300.0
Erdenes Oyu Tolgoi LLC
Disclosure of commitments and contingencies [Line Items]
Group interest (%)	34.00%
Turquoise Hill Resources Ltd
Disclosure of commitments and contingencies [Line Items]
Group interest (%)	66.00%
Minera Escondida Limitada
Disclosure of commitments and contingencies [Line Items]
Minera Escondida Limitada undrawn shareholder line of credit Rio Tinto share	$ 225.0	225.0
Group interest (%)	30.00%
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc \| Contingent liabilities related to joint ventures
Disclosure of commitments and contingencies [Line Items]
Contractual payments	$ 10.5
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc \| Contingent liabilities related to joint ventures \| Financial guarantee contracts
Disclosure of commitments and contingencies [Line Items]
Amounts guaranteed by parent companies	7,500.0	7,500.0
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc \| Contingent liabilities related to joint ventures \| Financial guarantee contracts \| Bonds
Disclosure of commitments and contingencies [Line Items]
Amounts guaranteed by parent companies	4,400.0	4,400.0
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc \| Contingent liabilities related to joint ventures \| Financial guarantee contracts \| Bonds
Disclosure of commitments and contingencies [Line Items]
Amounts guaranteed by parent companies	$ 1,200.0	$ 1,600.0

The amount of outstanding funds that the entity is obligated to repay.

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