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Financial instruments and risk management - Summary of fair value of financial instruments (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure Of Financial Instruments [Abstract] |  |
Short term borrowings, carrying value | $ (312) | $ (552)
Medium and long term borrowings, carrying value | (12,440) | (14,624)
Short term borrowings, fair value | (312) | (552)
Medium and long term borrowings, fair value | $ (13,554) | $ (16,385)

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- References No definition available. + Details
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- Definition The non-current portion of non-current borrowings. [Refer: Borrowings] + 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 current borrowings. [Refer: Borrowings] + 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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