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Share capital - Summary of share capital (Parenthetical) (Detail) - Rio Tinto plc [member] - shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Ordinary shares issued | 26,241 | 33,210 | 21,709
Number of shares bought back | 32,937,109 | 0 | 40,912,881
Treasury shares [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Ordinary shares issued | 147,126 | 743,380 |

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- Definition The number of shares issued by the entity. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 106 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_106_d&doctype=Standard -URIDate 2016-03-31 + Details
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