Financial instruments and risk management - Summary of financial assets by categories (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure of financial assets [Line Items]
Highly liquid financial assets held in managed investment funds classified as held for trading	$ 958	$ 250
Trade and other receivables	$ 2,985	3,047
Increase (decrease) due to corrections of prior period errors [member]
Disclosure of financial assets [Line Items]
Trade and other receivables		$ (385)

The amount of financial assets at fair value through profit or loss classified as held for trading. A financial asset is classified as held for trading if: (a) it is acquired principally for the purpose of selling it in the near term; (b) on initial recognition it is part of a portfolio of identified financial instruments that are managed together and for which there is evidence of a recent actual pattern of short-term profit-taking; or (c) it is a derivative (except for a derivative that is a financial guarantee contract or a designated and effective hedging instrument). [Refer: At fair value [member]; Financial assets at fair value through profit or loss]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph 8
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_a&doctype=Standard
-URIDate 2016-03-31

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant