Leases - Summary of information about leases of lessor in income statement (Detail) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosure of quantitative information about leases for lessor [abstract]
Interest on lease receivables	£ 6	£ 9	£ 11
Income from sub-leasing right-of-use assets (within other income)	£ 2	£ 7	£ 17

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 2021-01-01
-Paragraph 53
-Subparagraph f
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2021-en-r&anchor=para_53_f&doctype=Standard
-URIDate 2021-03-24

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