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Share capital - Rio Tinto Limited - Summary of share capital (Parenthetical) (Detail) - Rio Tinto Limited [member] - $ / shares | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2017 | Apr. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2015
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
Ordinary shares purchased and cancelled | 11,778,064 | 11,566,308 | 11,780,000 | 11,570,000
Price per purchased share | $ 63.67 | $ 48.44 |  |
Top of range [Member] |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
Number of shares bought back | 42,400,000 | 43,500,000 |  |

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