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Contingencies and commitments - Additional information (Detail) £ in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2017 GBP (£) | Dec. 31, 2016 USD ($)
Disclosure of commitments and contingencies [Line Items] |  |  |
Contractual capital commitments | $ 500.0 |  | $ 600.0
Turquoise Hill Resources Ltd (including Oyu Tolgoi LLC) [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Company of operation, Subsidiary | Turquoise Hill Resources Ltd | Turquoise Hill Resources Ltd |
Ownership percentage in subsidiary | 51.00% | 51.00% |
Oyu Tolgoi LLC [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Guarantee provided | $ 4,300.0 |  | 4,300.0
Turquoise Hill Resources Ltd [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Third party ownership interest in its associates | 66.00% | 66.00% |
Company of operation, Subsidiary | Oyu Tolgoi LLC | Oyu Tolgoi LLC |
Erdenes Oyu Tolgoi LLC [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Third party ownership interest in its associates | 34.00% | 34.00% |
Company of operation, Subsidiary | Oyu Tolgoi LLC | Oyu Tolgoi LLC |
United Kingdoms Financial Conduct Authority (FCA) [Member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Financial penalty | $ 36.4 | £ 27.4 |
Minera Escondida Limitada [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Minera Escondida Limitada undrawn shareholder line of credit Rio Tinto share | 225.0 |  |
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc [member] | Contingent liabilities related to joint ventures [Member] | Financial guarantee contracts [Member] |  |  |
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 [member] | Contingent liabilities related to joint ventures [Member] | Financial guarantee contracts [Member] | Bonds [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Amounts guaranteed by parent companies | 5,800.0 |  | 8,300.0
Rio Tinto Finance (USA) Limited and Rio Tinto Finance (USA) plc [member] | Contingent liabilities related to joint ventures [Member] | Financial guarantee contracts [Member] | Bonds [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Amounts guaranteed by parent companies | $ 2,100.0 |  | $ 1,900.0

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