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Dividends - Summary of number of shares dividend distributed (Detail) - shares shares in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Rio Tinto plc [member] |  |  |
Disclosure of Dividends [Line Items] |  |  |
Previous year final dividend number of shares | 1,374.6 | 1,373.9 | 1,412.7
Interim dividend number of shares | 1,366.1 | 1,374.4 | 1,395.2
Rio Tinto Limited [member] |  |  |
Disclosure of Dividends [Line Items] |  |  |
Previous year final dividend number of shares | 424.0 | 423.5 | 435.0
Interim dividend number of shares | 424.0 | 424.0 | 423.7

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