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Taxation - Summary of prima facie tax reconciliation (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Reconciliation Of Accounting Profit Multiplied By Applicable Tax Rates [Abstract] |  |  |
UK tax payable (receivable) rate | 19.00% | 19.00% | 20.00%
Groups share of profit of equity accounted units net of tax | $ 273 | $ 191 | $ 156

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- Definition The applicable income tax rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_ii&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Income tax on share of profit of equity accounted units. + References No definition available. + Details
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