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Share capital - Rio Tinto plc - Additional information (Detail) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
American depository receipts [member] |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
Value of shares purchased by employee share ownership trusts |  | $ 140.0 | $ 38.9 | $ 40.1
Rio Tinto plc [member] |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
Shares held in the employee share ownership trusts on behalf of Rio Tinto plc |  | 1,770,651 |  |
Number of shares bought back |  | 63,984,287 | 32,937,109 | 0
Rio Tinto plc [member] | Major ordinary share transactions [member] |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
Number of shares bought back | 10,956,767 |  |  |
Rio Tinto plc [member] | American depository receipts [member] |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |
ADRs held by the Employee share ownership Trust (ESOT) |  | 72,809 |  |

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