Name:	c070_AccumulatedFairValueHedgeAdjustmentOnHedgedItemIncludedInCarryingAmountAssetsLiabilities
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Balance Type:	credit
Period Type:	instant

The amount of deposits from banks and customer accounts at amortised cost, excluding cash collateral and settlement balances due.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The amount of sensitivity valuation analysis of assets and liabilities due to change in one or more unobservable inputs to reflect reasonably possible alternative assumptions.

No definition available.

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Data Type:	xbrli:monetaryItemType
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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: Financial instruments, class [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The description of the existence of third-party credit enhancement for liabilities measured at fair value and issued with an inseparable third-party credit enhancement. [Refer: At fair value [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=13&date=2018-03-01&anchor=para_98&doctype=Standard
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The description of whether third-party credit enhancement is reflected in the fair value measurement of liabilities measured at fair value and issued with an inseparable third-party credit enhancement. [Refer: At fair value [member]]

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

Name:	ifrs-full_DisclosureOfFinancialInstrumentsLineItems
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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. [Refer: Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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Name:	ifrs-full_IncreaseDecreaseInAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
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Data Type:	xbrli:monetaryItemType
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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; Financial instruments, class [member]]

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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_28_b&doctype=Standard
-URIDate 2018-03-16

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Data Type:	xbrli:monetaryItemType
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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; Financial instruments, class [member]]

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

Name:	ifrs-full_LiabilitiesMeasuredAtFairValueAndIssuedWithInseparableThirdpartyCreditEnhancementAxis=c070_BrokeredCertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
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Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level3OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_MeasurementAxis=ifrs-full_RecurringFairValueMeasurementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=c070_ExitPriceAdjustmentsDerivedFromMarketBidofferSpreadsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=c070_UncollateralisedDerivativeFundingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=c070_DerivativeCreditValuationAdjustmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=c070_DerivativeDebitValuationAdjustmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=c070_FinancialInstrumentsAtFairValueCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_ContinuingAndDiscontinuedOperationsAxis=c070_BarclaysUkMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=c070_BarclaysBankUkPlcMember
Namespace Prefix:
Data Type:	na
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