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Share capital - Rio Tinto plc - Summary of share capital (Parenthetical) (Detail) - Rio Tinto plc [member] $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) shares | Dec. 31, 2017 USD ($) £ / shares shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2016 USD ($) £ / shares shares | Dec. 31, 2015 USD ($) shares | Dec. 31, 2015 USD ($) £ / shares shares | Dec. 31, 2014 USD ($)
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |  |  |  |
Ordinary shares issued | 26,241 | 26,241 | 33,210 | 33,210 | 21,709 | 21,709 |
Number of shares bought back | 32,937,109 |  | 0 |  | 40,912,881 |  |
Share capital | $ | $ 220.0 | $ 220.0 | $ 224.0 | $ 224.0 | $ 224.0 | $ 224.0 | $ 230.0
Treasury stock reissued | $ | $ 2.0 |  | $ 4.0 |  | $ 13.0 |  |
Treasury shares [Member] |  |  |  |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |  |  |  |
Ordinary shares issued | 147,126 | 147,126 | 743,380 | 743,380 |  |  |
Rio Tinto Plc employee share based payment plans [member] |  |  |  |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |  |  |  |
Ordinary shares issued | 0 | 0 | 0 | 0 | 0 | 0 |
Exercise prices per share | £ / shares |  | $ 28.63 |  | $ 16.53 |  | $ 15.09 |
Market value per share | £ / shares |  | $ 37.78 |  | $ 32.23 |  | $ 32.37 |
Rio Tinto Plc employee share based payment plans [member] | Treasury shares [Member] |  |  |  |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |  |  |  |
Shares reissued from treasury | 147,126 |  | 743,380 |  | 789,887 |  |
Global employee share plan [member] |  |  |  |  |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |  |  |  |  |
Share capital | $ | $ 1.0 | $ 1.0 | $ 0.9 | $ 0.9 | $ 0.9 | $ 0.9 |

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