Name:	c070_AdditionalAllowanceRecognisedInProfitOrLoss
Namespace Prefix:	c070_
Data Type:	xbrli:monetaryItemType
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The amount of an allowance account used to record impairments to financial assets due to credit losses, including the amount of provisions other than provisions for employee benefits.

No definition available.

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

- References

No definition available.

Name:	c070_OnBalanceSheetAbstract
Namespace Prefix:	c070_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of additional allowance for credit losses of financial assets recognised in profit or loss. [Refer: Allowance account for credit losses of financial assets]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_16&doctype=Standard&book=b
-URIDate 2018-03-16

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

The amount of additional other provisions made. [Refer: Other provisions]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 37
-IssueDate 2018-01-01
-Paragraph 84
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2018-03-01&anchor=para_84_b&doctype=Standard
-URIDate 2018-03-16

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

The amount of an allowance account used to record impairments to financial assets due to credit losses. [Refer: Financial assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_16&doctype=Standard&book=b
-URIDate 2018-03-16

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

The amount of provisions other than provisions for employee benefits. [Refer: Provisions]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 37
-IssueDate 2018-01-01
-Paragraph 84
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2018-03-01&anchor=para_84_a&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 78
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_78_d&doctype=Standard
-URIDate 2018-03-16

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

The amount of financial assets reclassified into the at fair value through profit or loss category. [Refer: Financial assets at fair value through profit or loss]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 12
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_12&doctype=Standard&book=b
-URIDate 2018-03-16

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

Name:	srt_ConsolidatedEntitiesAxis=c070_BarclaysBankGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_ClassesOfProvisionsAxis=c070_UndrawnContractuallyCommittedFacilitiesAndGuaranteesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=ifrs-full_LoansAndReceivablesCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=ifrs-full_FinancialAssetsAvailableforsaleCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_CategoriesOfFinancialAssetsAxis=ifrs-full_FinancialAssetsAtFairValueThroughOtherComprehensiveIncomeCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_RetrospectiveApplicationAndRetrospectiveRestatementAxis=c070_IFRSs9Member
Namespace Prefix:
Data Type:	na
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Name:	ifrs-full_ClassesOfAssetsAxis=ifrs-full_OtherAssetsMember
Namespace Prefix:
Data Type:	na
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Period Type: