Disposal of Assets and other changes in organizational structure - Summary of Assets Classified as Held for Sale (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
PO and GBV [member]
Disclosure of information about assets and liabilities of disposal groups classified as held for sale [line items]
Divestment of interests	$ 973

The cash inflow from sales of interests in associates. [Refer: Associates [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2018-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2018-03-01&anchor=para_16&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_ProceedsFromSalesOfInterestsInAssociates
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration