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Principal joint ventures - Reconciliation of financial information for joint ventures by carrying value (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Disclosure Of Joint Ventures [Line Items] |  |
Net assets/(liabilities) | $ 49,823 | $ 51,115
Minera Escondida Limitada [member] |  |
Disclosure Of Joint Ventures [Line Items] |  |
Group interest | 30.00% | 30.00%
Net assets/(liabilities) | $ 9,343 | $ 10,230
Group's ownership interest | 2,803 | 3,069
Other adjustments |  | 4
Carrying value of Group's interest | $ 2,803 | $ 3,073
Sohar Aluminium Co. L.L.C. [member] |  |
Disclosure Of Joint Ventures [Line Items] |  |
Group interest | 20.00% | 20.00%
Net assets/(liabilities) | $ 2,240 | $ 2,060
Group's ownership interest | 448 | 412
Other adjustments | (1) | (3)
Carrying value of Group's interest | $ 447 | $ 409

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- Definition The amount of investments in joint ventures. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 10 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_10&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of investments in joint ventures accounted for using the equity method. [Refer: Joint ventures [member]; Non-current assets; Investments in joint ventures] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of assets less the amount of liabilities. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 1 -IssueDate 2017-01-01 -Paragraph IG63 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=1&date=2017-03-01&anchor=para_IG63&doctype=Implementation%20Guidance -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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