Deferred Taxation - Deferred tax liabilities and assets, prior to offsetting of balances (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	$ 6,440	$ 6,340
Deferred tax assets	(6,207)	(6,947)
Charged/(credited) to the income statement	695	(548)
Capital allowances [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	5,208	4,937
Deferred tax assets	(579)	(883)
Charged/(credited) to the income statement	278	(441)
Unremitted earnings [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	588	659
Capitalised interest [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	391	403
Unrealised exchange gains (losses) [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	31	40
Deferred tax assets	(317)	(342)
Charged/(credited) to the income statement	36	156
Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax liabilities	222	301
Deferred tax assets	(682)	(548)
Charged/(credited) to the income statement	(235)	150
Tax losses [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(2,282)	(2,246)
Charged/(credited) to the income statement	12	(122)
Provisions [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(1,731)	(2,040)
Charged/(credited) to the income statement	451	(279)
Post-retirement benefits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax assets	(616)	(888)
Charged/(credited) to the income statement	149	(6)
Tax on unremitted earnings [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Charged/(credited) to the income statement	$ 4	$ (6)

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 2016-01-13
-Paragraph 81
-Subparagraph g
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2016-03-30&anchor=para_81_g_ii&doctype=Standard
-URIDate 2016-03-31

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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 2016-01-13
-Paragraph 81
-Subparagraph g
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2016-03-30&anchor=para_81_g_i&doctype=Standard
-URIDate 2016-03-31

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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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