Leases - Summary of information about leases of lessor in income statement (Detail) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of quantitative information about leases for lessor [abstract]
Interest on lease receivables	£ 4	£ 5	£ 6
Income from subleasing right-of-use assets (within other income)	£ 6	£ 4	£ 2

The amount of income from subleasing right-of-use assets. Sublease is a transaction for which an underlying asset is re-leased by a lessee (‘intermediate lessor’) to a third party, and the lease (‘head lease’) between the head lessor and lessee remains in effect. [Refer: Right-of-use assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2023-01-01
-Paragraph 53
-Subparagraph f
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2023-en-r&anchor=para_53_f&doctype=Standard
-URIDate 2023-03-23

Name:	ifrs-full_IncomeFromSubleasingRightofuseAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration