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Intangible assets - Summary of exploration and evaluation expenditure (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Exploration And Evaluation Expenditure [Abstract] |  |  |
Net proceeds on disposal of undeveloped projects | $ 3 | $ 208 | $ 0

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- Definition The cash inflow from the disposal of exploration and evaluation assets. [Refer: Exploration and evaluation assets [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 7 -IssueDate 2016-01-13 -Paragraph 16 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2016-03-30&anchor=para_16&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition Exploration and evaluation expenditure [abstract] + References No definition available. + Details
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