Deferred Taxation - Deferred tax liabilities and assets, prior to offsetting of balances (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	$ 5,435	$ 6,440
Deferred tax assets	(4,899)	(6,207)
Charged/(credited) to the income statement	516	695
Capital allowances [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	4,408	5,208
Deferred tax assets	(154)	(579)
Charged/(credited) to the income statement	461	278
Unremitted earnings [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	454	588
Capitalised interest [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	259	391
Unrealised exchange gains (losses) [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	5	31
Deferred tax assets	(187)	(317)
Charged/(credited) to the income statement	57	36
Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	309	222
Deferred tax assets	(786)	(682)
Charged/(credited) to the income statement	50	(235)
Tax losses [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(1,894)	(2,282)
Charged/(credited) to the income statement	(30)	12
Provisions [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(1,585)	(1,731)
Charged/(credited) to the income statement	(19)	451
Post-retirement benefits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(293)	(616)
Charged/(credited) to the income statement	30	149
Tax on unremitted earnings [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Charged/(credited) to the income statement	$ (33)	$ 4

The amount of tax expense or income relating to changes in deferred tax liabilities and deferred tax assets, recognised in profit or loss. [Refer: Deferred tax assets; Deferred tax expense (income); Deferred tax liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2017-01-01
-Paragraph 81
-Subparagraph g
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_g_ii&doctype=Standard
-URIDate 2017-03-09

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The amount of deferred tax assets net of deferred tax liabilities, when the absolute amount of deferred tax assets is greater than the absolute amount of deferred tax liabilities. [Refer: Deferred tax assets; Deferred tax liabilities]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 12
-IssueDate 2017-01-01
-Paragraph 81
-Subparagraph g
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_g_i&doctype=Standard
-URIDate 2017-03-09

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- Definition

The amount of deferred tax liabilities net of deferred tax assets, when the absolute amount of deferred tax liabilities is greater than the absolute amount of deferred tax assets. [Refer: Deferred tax assets; Deferred tax liabilities]

+ References

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