Held for sale - Additional information (Detail) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Member]
Assets and Liabilities Held for Sale [line items]
Assets classified as held for sale	£ 2	£ 16

The amount of non-current assets or disposal groups classified as held for sale or as held for distribution to owners. [Refer: Non-current assets or disposal groups classified as held for distribution to owners; Non-current assets or disposal groups classified as held for sale]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2023-01-01
-Paragraph 54
-Subparagraph j
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2023-en-r&anchor=para_54_j&doctype=Standard
-URIDate 2023-03-23

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