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

The amount of decrease in the fair value measurement of assets and liabilities due to a change in one or more unobservable inputs to reflect reasonably possible alternative assumptions.

No definition available.

Name:	bbplc_DecreaseInFairValueMeasurementDueToChangeInOneOrMoreUnobservableInputsToReflectReasonablyPossibleAlternativeAssumptionsAssetsLiabilities
Namespace Prefix:	bbplc_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The increase (decrease) in fair value adjustments of derivatives during the period.

No definition available.

Name:	bbplc_IncreaseDecreaseInDerivativeFairValueAdjustments
Namespace Prefix:	bbplc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The amount of increase in the fair value measurement of assets and liabilities due to a change in one or more unobservable inputs to reflect reasonably possible alternative assumptions.

No definition available.

Name:	bbplc_IncreaseInFairValueMeasurementDueToChangeInOneOrMoreUnobservableInputsToReflectReasonablyPossibleAlternativeAssumptionsAssetsLiabilities
Namespace Prefix:	bbplc_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The aggregate difference between the fair value at initial recognition and the transaction price for financial instruments that is yet to be recognised in profit or loss. [Refer: Classes of financial instruments [domain]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 28
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_28_b&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 64
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_64_b&doctype=Standard
-URIDate 2025-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 64
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_64_b&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_AggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

The amount of deposit liabilities held by the entity at amortised cost. [Refer: Financial liabilities at amortised cost]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_55&doctype=Standard
-URIDate 2025-03-27

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

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

No definition available.

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

The increase (decrease) in the aggregate difference between the fair value at initial recognition and the transaction price of financial instruments yet to be recognised in profit or loss resulting from amounts recognised in profit or loss. [Refer: Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss; Classes of financial instruments [domain]]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph IG14
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_IG14&doctype=Implementation%20Guidance
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 28
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_28_b&doctype=Standard
-URIDate 2025-03-27

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 64
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_64_b&doctype=Standard
-URIDate 2025-03-27

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 64
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_64_b&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_IncreaseDecreaseThroughAmountsRecognisedInProfitOrLossAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The increase (decrease) in the aggregate difference between the fair value at initial recognition and the transaction price of financial instruments yet to be recognised in profit or loss resulting from new transactions. [Refer: Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss; Classes of financial instruments [domain]]

Name:	ifrs-full_IncreaseDecreaseThroughNewTransactionsAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The amount of transfers of assets into Level 3 of the fair value hierarchy. [Refer: Level 3 of fair value hierarchy [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 13
-IssueDate 2025-01-01
-Paragraph 93
-Subparagraph e
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2025-en-r&anchor=para_93_e_iv&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_TransfersIntoLevel3OfFairValueHierarchyAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of transfers of liabilities into Level 3 of the fair value hierarchy. [Refer: Level 3 of fair value hierarchy [member]]

Name:	ifrs-full_TransfersIntoLevel3OfFairValueHierarchyLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The amount of transfers out of Level 2 and into Level 1 of the fair value hierarchy of assets held at the end of the reporting period. [Refer: Level 1 of fair value hierarchy [member]; Level 2 of fair value hierarchy [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 13
-IssueDate 2025-01-01
-Paragraph 93
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2025-en-r&anchor=para_93_c&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_TransfersOutOfLevel2IntoLevel1OfFairValueHierarchyAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The amount of transfers out of Level 2 and into Level 1 of the fair value hierarchy of liabilities held at the end of the reporting period. [Refer: Level 1 of fair value hierarchy [member]; Level 2 of fair value hierarchy [member]]

Name:	ifrs-full_TransfersOutOfLevel2IntoLevel1OfFairValueHierarchyLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

Name:	ifrs-full_LiabilitiesMeasuredAtFairValueAndIssuedWithInseparableThirdpartyCreditEnhancementAxis=bbplc_BrokeredCertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=bbplc_DerivativeCreditValuationAdjustmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level3OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=bbplc_FinancialInstrumentsAtFairValueCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=bbplc_FinancialInstrumentsAtAmortisedCostCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=bbplc_ExitPriceAdjustmentsDerivedFromMarketBidOfferSpreadsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=bbplc_UncollateralisedDerivativeFundingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=bbplc_DerivativeDebitValuationAdjustmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: