Lessee disclosures - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Leases [Abstract]
Payments of lease liabilities, classified as financing activities	£ 215	£ 210

The cash outflow for payment of lease liabilities, classified as financing activities. [Refer: Lease liabilities]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2023-01-01
-Paragraph 17
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2023-en-r&anchor=para_17_e&doctype=Standard
-URIDate 2023-03-23

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