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Finance income and finance costs - Summary of finance income and finance costs (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Material Income And Expense [Abstract] |  |
Premium charges for redemption of bonds | $ 238 | $ 441
Unamortized Debt Issuance Costs and Fees | 14 | 42
Fair value hedge adjustment | $ 4 | $ (159)

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- References No definition available. + Details
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- Definition The cash outflow for debt issue costs. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 7 -IssueDate 2016-01-13 -Paragraph 17 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2016-03-30&anchor=para_17&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition Fair value hedge adjustment. + References No definition available. + Details
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- Definition The premium charge associated with the redemption of bonds. + References No definition available. + Details
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