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Contingencies and commitments - Additional information (Detail) £ in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2017 GBP (£)
Disclosure of commitments and contingencies [Line Items] |  |  |
Contractual capital commitments | $ 400.0 | $ 500.0 |
Borrowings | $ 12,752.0 | 15,176.0 |
Turquoise Hill Resources Ltd (including Oyu Tolgoi LLC) [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Ownership percentage in subsidiary | 51.00% |  |
Company of operation, Subsidiary | Turquoise Hill Resources Ltd |  |
Oyu Tolgoi LLC [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Borrowings | $ 4,300.0 | 4,300.0 |
Erdenes Oyu Tolgoi LLC [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Percentage of ownership interest exchanged in joint venture | 34.00% |  |
Company of operation | Oyu Tolgoi LLC |  |
Turquoise Hill Resources Ltd [member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Percentage of ownership interest exchanged in joint venture | 66.00% |  |
Company of operation | Oyu Tolgoi LLC |  |
Contingent liabilities related to joint ventures [Member] |  |  |
Disclosure of commitments and contingencies [Line Items] |  |  |
Ownership percentage in subsidiary | 100.00% |  |
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 | $ 225.0 |
Percentage of ownership interest exchanged in joint venture | 30.00% | 30.00% | 30.00%
Company of operation | Minera Escondida Limitada |  |
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 | 4,400.0 | 5,800.0 |
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 | $ 1,600.0 | $ 2,100.0 |

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