Insurance service expense - Narrative (Details) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2022
Insurance Contracts [Abstract]
Derecognized CSM relating to contracts modified				£ 399
CSM relating to new contracts recognised	£ 1,730
CSM increase				1,331
Increase (decrease) through changes that relate to future service, insurance contracts liability (asset)	£ (22)	£ (1,222)	£ (266)
CSM expense		£ 1,015	£ 227	£ 1,242

The increase (decrease) in insurance contracts liability (asset) resulting from changes that relate to future service. [Refer: Insurance contracts liability (asset)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2023-01-01
-Name IFRS
-Number 17
-IssueDate 2022-03-24
-Paragraph 103
-Subparagraph b
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=17&code=ifrs-tx-2022-en-r&anchor=para_103_b_iv&doctype=Standard
-URIDate 2022-03-24

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2023-01-01
-Name IFRS
-Number 17
-IssueDate 2022-03-24
-Paragraph 104
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=17&code=ifrs-tx-2022-en-r&anchor=para_104_a&doctype=Standard
-URIDate 2022-03-24

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