General Information - Impact of IFRS 15 on Group Statement of Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of impact of initial application of new accounting standards [line item]
Exchange losses on retranslation of foreign operations, tax	$ (2)	$ (1)	$ 3
IFRS 15 [member]
Disclosure of impact of initial application of new accounting standards [line item]
Exchange losses on retranslation of foreign operations, tax		$ 1

The amount of income tax relating to amounts recognised in other comprehensive income in relation to exchange differences on the translation of financial statements of foreign operations. [Refer: Other comprehensive income; Reserve of exchange differences on translation]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2018-01-01
-Paragraph 81
-Subparagraph ab
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2018-03-01&anchor=para_81_ab&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 90
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_90&doctype=Standard
-URIDate 2018-03-16

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