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Taxation - Summary of tax relating to components of other comprehensive income or loss (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Relating To Components Of Other Comprehensive Income That Will Be Reclassified To Profit Or Loss [Abstract] |  |  |
– Cash flow hedge fair value (gains)/losses | $ (54) | $ (1) | $ 4
Tax (charge)/credit on actuarial gains and losses on post-retirement benefit plans | (271) | (12) | 29
Adjustments to deferred tax on post-retirement benefit plans due to changes in corporate tax rates in the US and France |  | (140) |
Tax relating to components of other comprehensive income/(loss) for the year | $ (325) | $ (153) | $ 33

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- Definition The amount of income tax relating to amounts recognised in other comprehensive income in relation to cash flow hedges. [Refer: Cash flow hedges [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph ab -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_ab&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 90 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_90&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of income tax relating to amounts recognised in other comprehensive income. [Refer: Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph ab -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_ab&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 90 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_90&doctype=Standard -URIDate 2017-03-09 + Details
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- References No definition available. + Details
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- Definition The amount of income tax relating to amounts recognised in other comprehensive income in relation to remeasurements of defined benefit plans. [Refer: Other comprehensive income; Reserve of remeasurements of defined benefit plans; Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph ab -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_ab&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 90 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_90&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Income tax relating to Adjustments to deferred tax on post-retirement benefit plans due to changes in corporate tax rates in the US and France. + References No definition available. + Details
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