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Other reserves and retained earnings - Summary of other reserves and retained earnings (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | $ 12,284 |  |  |  |  |
Change in equity interest held by Rio Tinto | [1] |  |  |  |  | $ (165) |
Own shares purchased from Rio Tinto shareholders to satisfy share options |  | (254) | [2] | $ (82) | [2] | (80) |
Companies no longer consolidated |  |  |  | (2) |  | 8 |
Ending balance |  | 8,661 |  | 12,284 |  |  |
Parent and subsidiaries currency translation and exchange adjustments |  | 213 |  | (70) |  |  |
Beginning balance |  | 23,761 |  |  |  |  |
Tax relating to components of other comprehensive income |  | (325) |  | (153) |  | 33 |
Dividends |  | (5,771) |  | (4,653) |  | (3,077) |
Employee share options and other IFRS 2 charges to the income statement |  | 111 |  | 98 |  | 125 |
Ending balance |  | 27,025 |  | 23,761 |  |  |
Capital redemption reserve [Member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | 38 |  | 34 |  | 34 |
Own shares purchased and cancelled |  | 9 |  | 4 |  |  |
Ending balance |  | 47 |  | 38 |  | 34 |
Cash flow hedge reserve [member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | 32 |  | 32 |  |  |
Adjustment for transition to new accounting standards (note 45) |  | (4) |  |  |  |  |
Cash flow hedge gains/(losses) |  | 156 |  | 62 |  | (88) |
Cash flow hedge losses/(gains) transferred to the income statement |  | 40 |  | (62) |  | 116 |
Tax on the above |  | (54) |  |  |  | 4 |
Transfers and other movements |  | 25 |  |  |  |  |
Ending balance |  | 195 |  | 32 |  | 32 |
Available for sale revaluation reserves [member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | 20 |  | (126) |  | (139) |
Adjustment for transition to new accounting standards (note 45) |  | (20) |  |  |  |  |
Gains on available for sale securities |  |  |  | 19 |  | 13 |
Losses on available for sale securities transferred to the income statement |  |  |  | 6 |  |  |
Tax on the above |  |  |  | (1) |  |  |
Transfers and other movements |  |  |  | 122 |  |  |
Ending balance |  |  |  | 20 |  | (126) |
Fair Value through Other Comprehensive Income reserve [member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Adjustment for transition to new accounting standards (note 45) |  | 8 |  |  |  |  |
Losses on equity investments |  | (11) |  |  |  |  |
Transfers to retained earnings |  | (3) |  |  |  |  |
Ending balance |  | (6) |  |  |  |  |
Cost of Hedging Reserve [Member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Adjustment for transition to new accounting standards (note 45) |  | 26 |  |  |  |  |
Cost of hedging deferred to reserves during the year |  | (36) |  |  |  |  |
Transfer of cost of hedging to the income statement |  | (3) |  |  |  |  |
Ending balance |  | (13) |  |  |  |  |
Other reserves [member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | 11,714 |  | 11,861 |  | 11,735 |
Change in equity interest held by Rio Tinto |  |  |  |  |  | 108 |
Own shares purchased from Rio Tinto Limited shareholders to satisfy share options |  | (114) |  | (64) |  | (43) |
Own shares purchased from Rio Tinto shareholders to satisfy share options |  | 52 |  | 31 |  | 58 |
Deferred tax on share options |  | (2) |  | 10 |  | 3 |
Companies no longer consolidated |  |  |  | (124) |  |  |
Ending balance |  | 11,650 |  | 11,714 |  | 11,861 |
Foreign currency translation reserve [member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Beginning balance |  | 12,284 |  | 9,216 |  |  |
Ending balance |  | 8,661 |  | 12,284 |  | 9,216 |
Beginning balance |  | 480 |  | (2,585) |  | (2,491) |
Parent and subsidiaries currency translation and exchange adjustments |  | (3,658) |  | 2,942 |  | (204) |
Equity accounted units currency translation adjustments |  | (48) |  | 34 |  | 11 |
Currency translation reclassified on disposal |  | 14 |  | 78 |  | 99 |
Transfers and other movements |  |  |  | 11 |  |  |
Ending balance |  | (3,212) |  | 480 |  | (2,585) |
Retained earnings [Member] |  |  |  |  |  |  |
Disclosure Of Other Reserves And Retained Earnings [Line Items] |  |  |  |  |  |  |
Change in equity interest held by Rio Tinto |  | 60 |  | 43 |  | 40 | [1]
Own shares purchased from Rio Tinto Limited shareholders to satisfy share options |  | (22) |  | (133) |  |  |
Own shares purchased from Rio Tinto shareholders to satisfy share options |  | (140) | [2] | (18) | [2] | (37) |
Companies no longer consolidated |  |  |  | 130 |  |  |
Beginning balance |  | 23,761 |  | 21,631 |  | 19,736 |
Adjustment for transition to new accounting standards (note 45) |  | (179) |  |  |  |  |
Parent and subsidiaries' profit for the year |  | 13,125 |  | 8,423 |  | 4,298 |
Equity accounted units' profit after tax for the year |  | 513 |  | 339 |  | 319 |
Actuarial gains/(losses) |  | 894 |  | 1 |  | (94) |
Tax relating to components of other comprehensive income |  | (269) |  | (150) |  | 30 |
Total comprehensive income for the year |  | 14,263 |  | 8,613 |  | 4,553 |
Share buy-back programme |  | (5,423) |  | (2,312) |  |  |
Dividends |  | (5,356) |  | (4,250) |  | (2,725) |
Companies no longer consolidated |  |  |  | 130 |  |  |
Employee share options and other IFRS 2 charges to the income statement |  | 61 |  | 57 |  | 64 |
Transfer from FVOCI reserve |  | 3 |  |  |  |  |
Transfers and other movements |  | (25) |  | (133) |  |  |
Ending balance |  | $ 27,025 |  | $ 23,761 |  | $ 21,631 |
[1] | The restructure of Coal & Allied Industries Limited completed on 3 February 2016. The restructure involved the exchange of a 32.4% interest in Hunter Valley Operations mine for an additional 20% shareholding in Coal & Allied Industries Limited, increasing Rio Tinto’s shareholding of Coal & Allied Industries Limited from 80% to 100%. Rio Tinto sold its 100% interest in Coal & Allied Industries Limited on 1 September 2017.
[2] | Net of contributions received from employees for share options.

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- Definition A component of equity representing the accumulated portion of gain (loss) on a hedging instrument that is determined to be an effective hedge for cash flow hedges. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_78_e&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 9 -IssueDate 2017-01-01 -Paragraph 6.5.11 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=9&date=2017-03-01&anchor=para_6.5.11&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition A component of equity representing exchange differences on translation of financial statements of foreign operations recognised in other comprehensive income and accumulated in equity. [Refer: Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 21 -IssueDate 2017-01-01 -Paragraph 52 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=21&date=2017-03-01&anchor=para_52_b&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition A component of equity representing accumulated gains and losses from investments in equity instruments that the entity has designated at fair value through other comprehensive income. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Note Effective 2018-01-01 -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_78_e&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition A component of equity representing the reserve of gains and losses on financial assets measured at fair value through other comprehensive income. [Refer: Financial assets measured at fair value through other comprehensive income; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Note Effective 2018-01-01 -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_78_e&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition A component of equity representing accumulated gains and losses on remeasuring available-for-sale financial assets. [Refer: Financial assets available-for-sale] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Note Expiry date 2018-01-01 -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-02&anchor=para_78_e&doctype=Standard&book=B -URIDate 2017-03-09 + Details
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- Definition A component of equity representing the entity's cumulative undistributed earnings or deficit. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_78_e&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph IG6 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_IG6&doctype=Implementation%20Guidance -URIDate 2017-03-09 + Details
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