Credit impairment charges / (releases) - Modification of financial assets (Narrative) (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021
Disclosure of impairment loss and reversal of impairment loss [abstract]
Financial assets written and subject to enforcement activity, contractual amount outstanding	£ 512	£ 752
Amortised cost before modification	2,237	3,260
Net modification loss	1	2
Carrying amount of financial assets for which loss allowance has changed to 12-month measurement	£ 1,077	£ 419

No definition available.

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

- Definition

The amortised cost before the modification of financial assets for which the contractual cash flows have been modified during the reporting period while they had a loss allowance measured at an amount equal to lifetime expected credit losses. [Refer: Financial assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2022-03-24
-Paragraph 35J
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2022-en-r&anchor=para_35J_a&doctype=Standard
-URIDate 2022-03-24

+ Details

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

- Definition

The net modification gain (loss) on financial assets for which the contractual cash flows have been modified during the reporting period while they had a loss allowance measured at an amount equal to lifetime expected credit losses. [Refer: Financial assets]

+ References

+ Details

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

- Definition

The gross carrying amount of financial assets that have been modified since initial recognition at a time when the loss allowance was measured at an amount equal to lifetime expected credit losses and for which the loss allowance has changed during the reporting period to an amount equal to 12-month expected credit losses. [Refer: Financial assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2022-03-24
-Paragraph 35J
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2022-en-r&anchor=para_35J_b&doctype=Standard
-URIDate 2022-03-24

+ Details

Name:	ifrs-full_FinancialAssetsWithModifiedContractualCashFlowsWhileLossAllowanceMeasuredAtLifetimeExpectedCreditLossesForWhichLossAllowanceChangedDuringReportingPeriodTo12monthExpectedCreditLossesGrossCarryingAmount
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The contractual amount outstanding on financial assets that were written off during the reporting period and are still subject to enforcement activity. [Refer: Financial assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2022-03-24
-Paragraph 35L
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2022-en-r&anchor=para_35L&doctype=Standard
-URIDate 2022-03-24

+ Details

Name:	ifrs-full_FinancialAssetsWrittenOffDuringReportingPeriodAndStillSubjectToEnforcementActivityContractualAmountOutstanding
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant