Subordinated liabilities - Summary (Details) - GBP (£) £ in Millions	Dec. 31, 2022	Dec. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Undated subordinated liabilities	£ 538	£ 795
Dated subordinated liabilities	38,236	31,873
Total subordinated liabilities	£ 38,774	£ 32,668

Subordinated Liabilities, Including Those Designated At Fair Value

No definition available.

Name:	bbplc_SubordinatedLiabilitiesIncludingThoseDesignatedAtFairValue
Namespace Prefix:	bbplc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of subordinated liabilities that have a specified repayment date. [Refer: Subordinated liabilities]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2022-03-24

+ Details

Name:	ifrs-full_DatedSubordinatedLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	ifrs-full_SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of subordinated liabilities that do not have a specified repayment date. [Refer: Subordinated liabilities]

+ References

+ Details

Name:	ifrs-full_UndatedSubordinatedLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant