Significant Accounting Policies - Impact of IFRS 16 on Group Statement of Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of impact of initial application of new accounting standards [line item]
Exchange losses on retranslation of foreign operations, tax	$ (3)	$ (2)	$ (1)
IFRS 16 [member]
Disclosure of impact of initial application of new accounting standards [line item]
Exchange losses on retranslation of foreign operations, tax		$ 2	$ 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 2019-01-01
-Paragraph 81
-Subparagraph ab
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_ab&doctype=Standard
-URIDate 2019-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 90
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_90&doctype=Standard
-URIDate 2019-03-27

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