Staff costs and Directors' remuneration - Additional Information (Detail) $ in Millions	Dec. 31, 2020 USD ($)
Text block [abstract]
Government subsidies received	$ 36

The amount of assistance by government in the form of transfers of resources to an entity in return for past or future compliance with certain conditions relating to the operating activities of the entity, recognised as deferred income. They exclude those forms of government assistance that cannot reasonably have a value placed upon them and transactions with government that cannot be distinguished from the normal trading transactions of the entity. [Refer: Government [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_55&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_GovernmentGrants
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant