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Share capital - Rio Tinto Limited - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Rio Tinto Limited shares were held by Rio Tinto plc | 0 | 0 | 0
Rio Tinto Limited [member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Value of shares purchased by employee share ownership trusts | $ 114.0 | $ 37.5 | $ 48.5
Rio Tinto Limited shares were held by Rio Tinto plc | 1,416,728 |  |

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