v3.26.1
Credit Risk - Disclosure of loans and advances at amortised cost by geography (Details)
£ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2026
GBP (£)
Jun. 30, 2025
GBP (£)
Dec. 31, 2025
GBP (£)
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loan loss rate 0.0062   0.0052
Total income statement charges for the period £ 1,394 £ 1,112 £ 2,279
Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (5,969)   (5,727)
Financial assets at fair value through profit or loss, designated upon initial recognition or subsequently | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Exposure to credit risk on loan commitments and financial guarantee contracts 32,300   22,200
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 868,582   £ 857,365
Coverage ratio 0.007   0.007
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 874,551   £ 863,092
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (5,969)   (5,727)
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Stage 1      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 816,224   £ 806,150
Coverage ratio 0.001   0.001
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 817,293   £ 807,198
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,069)   (1,048)
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 46,733   £ 45,551
Coverage ratio 0.041   0.041
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 48,721   £ 47,508
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,988)   (1,957)
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 5,599   £ 5,620
Coverage ratio 0.342   0.326
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 8,511   £ 8,342
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (2,912)   (2,722)
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 26   £ 44
Coverage ratio 0   0
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 26   £ 44
Total of loans and advances at amortised cost including off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Loans and advances at amortised cost including debt securities      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 444,820   £ 429,998
Coverage ratio 0.012   0.012
Loans and advances at amortised cost including debt securities | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 450,356   £ 435,309
Loans and advances at amortised cost including debt securities | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (5,536)   (5,311)
Loans and advances at amortised cost including debt securities | Stage 1      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 409,180   £ 395,801
Coverage ratio 0.002   0.002
Loans and advances at amortised cost including debt securities | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 410,091   £ 396,705
Loans and advances at amortised cost including debt securities | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (911)   (904)
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 2      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 30,821   £ 29,318
Coverage ratio 0.054   0.055
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 32,571   £ 31,035
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,750)   (1,717)
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 excluding POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 4,798   £ 4,840
Coverage ratio 0.375   0.357
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 7,673   £ 7,530
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (2,875)   (2,690)
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 21   £ 39
Coverage ratio 0   0
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 21   £ 39
Loans and advances at amortised cost including debt securities | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Loans and advances | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 371,301   £ 361,523
Coverage ratio 0.015   0.014
Loans and advances | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 270,638   £ 264,725
Coverage ratio 0.008   0.008
Loans and advances | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 100,663   £ 96,798
Coverage ratio 0.031   0.032
Loans and advances | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 376,817   £ 366,812
Loans and advances | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 272,951   266,776
Loans and advances | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 103,866   100,036
Loans and advances | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (5,516)   (5,289)
Loans and advances | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (2,313)   (2,051)
Loans and advances | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (3,203)   (3,238)
Loans and advances | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 336,829   £ 327,688
Coverage ratio 0.003   0.003
Loans and advances | Stage 1 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 244,438   £ 238,387
Coverage ratio 0.002   0.002
Loans and advances | Stage 1 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 92,391   £ 89,301
Coverage ratio 0.005   0.005
Loans and advances | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 337,729   £ 328,579
Loans and advances | Stage 1 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 244,831   238,796
Loans and advances | Stage 1 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 92,898   89,783
Loans and advances | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (900)   (891)
Loans and advances | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (393)   (409)
Loans and advances | Stage 1 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (507)   (482)
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 29,653   £ 28,956
Coverage ratio 0.055   0.056
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 23,237   £ 23,376
Coverage ratio 0.034   0.032
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 6,416   £ 5,580
Coverage ratio 0.126   0.144
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 31,394   £ 30,664
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 24,051   24,148
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 7,343   6,516
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,741)   (1,708)
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (814)   (772)
Loans and advances | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (927)   (936)
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 4,798   £ 4,840
Coverage ratio 0.375   0.357
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,942   £ 2,923
Coverage ratio 0.273   0.229
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,856   £ 1,917
Coverage ratio 0.488   0.487
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 7,673   £ 7,530
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 4,048   3,793
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 3,625   3,737
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (2,875)   (2,690)
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,106)   (870)
Loans and advances | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,769)   (1,820)
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 21   £ 39
Coverage ratio 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 21   £ 39
Coverage ratio 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 21   £ 39
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 21   39
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Loans and advances | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 181,669   177,450
Retail mortgages | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (127)   (117)
Retail mortgages | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 181,542   £ 177,333
Coverage ratio 0.001   0.001
Retail mortgages | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 179,508   £ 175,327
Coverage ratio 0.001   0.001
Retail mortgages | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,034   £ 2,006
Coverage ratio 0.015   0.013
Retail mortgages | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 181,669   £ 177,450
Retail mortgages | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 179,605   175,418
Retail mortgages | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,064   2,032
Retail mortgages | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (127)   (117)
Retail mortgages | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (97)   (91)
Retail mortgages | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (30)   (26)
Retail mortgages | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 165,632   161,654
Retail mortgages | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (19)   (17)
Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 165,613   £ 161,637
Coverage ratio 0   0
Retail mortgages | Stage 1 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 163,955   £ 159,810
Coverage ratio 0   0
Retail mortgages | Stage 1 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,658   £ 1,827
Coverage ratio 0.002   0.001
Retail mortgages | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 165,632   £ 161,654
Retail mortgages | Stage 1 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 163,971   159,825
Retail mortgages | Stage 1 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,661   1,829
Retail mortgages | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (19)   (17)
Retail mortgages | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (16)   (15)
Retail mortgages | Stage 1 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (3)   (2)
Retail mortgages | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 14,100   13,829
Retail mortgages | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (21)   (16)
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 14,079   £ 13,813
Coverage ratio 0.001   0.001
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 13,849   £ 13,741
Coverage ratio 0.001   0.001
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 230   £ 72
Coverage ratio 0.004   0
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 14,100   £ 13,829
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 13,869   13,757
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 231   72
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (21)   (16)
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (20)   (16)
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1)   0
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,937   1,967
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (87)   (84)
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,850   £ 1,883
Coverage ratio 0.045   0.043
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,704   £ 1,776
Coverage ratio 0.035   0.033
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 146   £ 107
Coverage ratio 0.151   0.183
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,937   £ 1,967
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,765   1,836
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 172   131
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (87)   (84)
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (61)   (60)
Retail mortgages | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (26)   (24)
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail mortgages | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail credit cards | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 41,103   40,281
Retail credit cards | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (3,436)   (3,329)
Retail credit cards | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 37,667   £ 36,952
Coverage ratio 0.084   0.083
Retail credit cards | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 16,679   £ 16,425
Coverage ratio 0.045   0.043
Retail credit cards | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 20,988   £ 20,527
Coverage ratio 0.112   0.112
Retail credit cards | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 41,103   £ 40,281
Retail credit cards | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 17,468   17,168
Retail credit cards | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 23,635   23,113
Retail credit cards | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (3,436)   (3,329)
Retail credit cards | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (789)   (743)
Retail credit cards | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (2,647)   (2,586)
Retail credit cards | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 34,108   33,723
Retail credit cards | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (582)   (566)
Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 33,526   £ 33,157
Coverage ratio 0.017   0.017
Retail credit cards | Stage 1 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 14,897   £ 14,751
Coverage ratio 0.011   0.011
Retail credit cards | Stage 1 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 18,629   £ 18,406
Coverage ratio 0.022   0.021
Retail credit cards | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 34,108   £ 33,723
Retail credit cards | Stage 1 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 15,067   14,922
Retail credit cards | Stage 1 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 19,041   18,801
Retail credit cards | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (582)   (566)
Retail credit cards | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (170)   (171)
Retail credit cards | Stage 1 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (412)   (395)
Retail credit cards | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 4,865   4,479
Retail credit cards | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,215)   (1,194)
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 3,650   £ 3,285
Coverage ratio 0.250   0.267
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,655   £ 1,545
Coverage ratio 0.206   0.205
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,995   £ 1,740
Coverage ratio 0.282   0.314
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 4,865   £ 4,479
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,085   1,943
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,780   2,536
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,215)   (1,194)
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (430)   (398)
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (785)   (796)
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,117   2,055
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,639)   (1,569)
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 478   £ 486
Coverage ratio 0.774   0.764
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 114   £ 105
Coverage ratio 0.624   0.624
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 364   £ 381
Coverage ratio 0.799   0.785
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,117   £ 2,055
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 303   279
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,814   1,776
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,639)   (1,569)
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (189)   (174)
Retail credit cards | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,450)   (1,395)
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 13   24
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 13   £ 24
Coverage ratio 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 13   £ 24
Coverage ratio 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 13   £ 24
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 13   24
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail credit cards | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail other | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 14,771   14,431
Retail other | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (536)   (517)
Retail other | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 14,235   £ 13,914
Coverage ratio 0.036   0.036
Retail other | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 11,135   £ 11,190
Coverage ratio 0.043   0.042
Retail other | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 3,100   £ 2,724
Coverage ratio 0.010   0.010
Retail other | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 14,771   £ 14,431
Retail other | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 11,640   11,680
Retail other | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 3,131   2,751
Retail other | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (536)   (517)
Retail other | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (505)   (490)
Retail other | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (31)   (27)
Retail other | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 12,297   12,349
Retail other | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (110)   (101)
Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 12,187   £ 12,248
Coverage ratio 0.009   0.008
Retail other | Stage 1 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 9,580   £ 9,769
Coverage ratio 0.011   0.010
Retail other | Stage 1 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,607   £ 2,479
Coverage ratio 0.003   0.001
Retail other | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 12,297   £ 12,349
Retail other | Stage 1 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 9,683   9,867
Retail other | Stage 1 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,614   2,482
Retail other | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (110)   (101)
Retail other | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (103)   (98)
Retail other | Stage 1 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (7)   (3)
Retail other | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,041   1,718
Retail other | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (190)   (183)
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,851   £ 1,535
Coverage ratio 0.093   0.107
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,413   £ 1,334
Coverage ratio 0.115   0.118
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 438   £ 201
Coverage ratio 0.014   0.024
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,041   £ 1,718
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,597   1,512
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 444   206
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (190)   (183)
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (184)   (178)
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (6)   (5)
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 425   349
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (236)   (233)
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 189   £ 116
Coverage ratio 0.555   0.668
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 134   £ 72
Coverage ratio 0.619   0.748
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 55   £ 44
Coverage ratio 0.247   0.302
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 425   £ 349
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 352   286
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 73   63
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (236)   (233)
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (218)   (214)
Retail other | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (18)   (19)
Retail other | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 8   15
Retail other | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 8   £ 15
Coverage ratio 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 8   £ 15
Coverage ratio 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 8   £ 15
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 8   15
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Retail other | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 139,274   134,650
Corporate debt | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,417)   (1,326)
Corporate debt | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 137,857   £ 133,324
Coverage ratio 0.010   0.010
Corporate debt | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 63,316   £ 61,783
Coverage ratio 0.014   0.012
Corporate debt | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 74,541   £ 71,541
Coverage ratio 0.007   0.008
Corporate debt | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 139,274   £ 134,650
Corporate debt | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 64,238   62,510
Corporate debt | Financial assets at amortised cost | Gross exposure | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 12,400   12,400
Corporate debt | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 75,036   72,140
Corporate debt | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (1,417)   (1,326)
Corporate debt | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (922)   (727)
Corporate debt | Financial assets at amortised cost | Impairment allowance | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ (301)   £ (326)
Corporate debt | Financial assets at amortised cost | Impairment allowance | UK | CGU excluding Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Coverage ratio 0.012   0.008
Corporate debt | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ (495)   £ (599)
Corporate debt | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 125,692   120,853
Corporate debt | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (189)   (207)
Corporate debt | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 125,503   £ 120,646
Coverage ratio 0.002   0.002
Corporate debt | Stage 1 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 56,006   £ 54,057
Coverage ratio 0.002   0.002
Corporate debt | Stage 1 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 69,497   £ 66,589
Coverage ratio 0.001   0.001
Corporate debt | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 125,692   £ 120,853
Corporate debt | Stage 1 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 56,110   54,182
Corporate debt | Stage 1 | Financial assets at amortised cost | Gross exposure | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 9,700   9,300
Corporate debt | Stage 1 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 69,582   66,671
Corporate debt | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (189)   (207)
Corporate debt | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (104)   (125)
Corporate debt | Stage 1 | Financial assets at amortised cost | Impairment allowance | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (47)   (62)
Corporate debt | Stage 1 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (85)   (82)
Corporate debt | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 10,388   10,638
Corporate debt | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (315)   (315)
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 10,073   £ 10,323
Coverage ratio 0.030   0.030
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 6,320   £ 6,756
Coverage ratio 0.028   0.026
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 3,753   £ 3,567
Coverage ratio 0.035   0.036
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 10,388   £ 10,638
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 6,500   6,936
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 2,000   2,300
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 3,888   3,702
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (315)   (315)
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (180)   (180)
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (47)   (50)
Corporate debt | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (135)   (135)
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 3,194   3,159
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (913)   (804)
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 2,281   £ 2,355
Coverage ratio 0.286   0.255
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 990   £ 970
Coverage ratio 0.392   0.303
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,291   £ 1,385
Coverage ratio 0.176   0.216
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 3,194   £ 3,159
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,628   1,392
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 1,566   1,767
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (913)   (804)
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (638)   (422)
Corporate debt | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (275)   (382)
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | UK      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance | Rest of the world      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Corporate debt | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost | Gross exposure | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 700   800
Corporate debt | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost | Impairment allowance | UK | Business Banking      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (207)   (214)
Debt securities at amortised cost | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 73,519   £ 68,475
Coverage ratio 0   0
Debt securities at amortised cost | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 73,539   £ 68,497
Debt securities at amortised cost | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (20)   (22)
Debt securities at amortised cost | Stage 1 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 72,351   £ 68,113
Coverage ratio 0   0
Debt securities at amortised cost | Stage 1 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 72,362   £ 68,126
Debt securities at amortised cost | Stage 1 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (11)   (13)
Debt securities at amortised cost | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,168   £ 362
Coverage ratio 0.008   0.024
Debt securities at amortised cost | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 1,177   £ 371
Debt securities at amortised cost | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (9)   (9)
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 excluding POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Coverage ratio 0   0
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 0   £ 0
Debt securities at amortised cost | Lifetime expected credit losses | Stage 3 POCI | Financial assets at amortised cost | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Off balance sheet loan commitments and financial guarantee contracts      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 423,762   £ 427,367
Coverage ratio 0.001   0.001
Off balance sheet loan commitments and financial guarantee contracts | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 424,195   £ 427,783
Off balance sheet loan commitments and financial guarantee contracts | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (433)   (416)
Off balance sheet loan commitments and financial guarantee contracts | Stage 1      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 407,044   £ 410,349
Coverage ratio 0   0
Off balance sheet loan commitments and financial guarantee contracts | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 407,202   £ 410,493
Off balance sheet loan commitments and financial guarantee contracts | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (158)   (144)
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 15,912   £ 16,233
Coverage ratio 0.015   0.015
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 16,150   £ 16,473
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (238)   (240)
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 801   £ 780
Coverage ratio 0.044   0.039
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 838   £ 812
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 excluding POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (37)   (32)
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 5   £ 5
Coverage ratio 0   0
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ 5   £ 5
Off balance sheet loan commitments and financial guarantee contracts | Lifetime expected credit losses | Stage 3 POCI | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 0   0
Other financial assets subject to impairment | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 286,400   224,100
Other financial assets subject to impairment | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (151)   (150)
Other financial assets subject to impairment | Stage 1 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 285,500   222,400
Other financial assets subject to impairment | Stage 1 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (17)   (18)
Other financial assets subject to impairment | Lifetime expected credit losses | Stage 2 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 800   1,600
Other financial assets subject to impairment | Lifetime expected credit losses | Stage 2 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances (10)   (8)
Other financial assets subject to impairment | Lifetime expected credit losses | Stage 3 | Gross exposure      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances 127   127
Other financial assets subject to impairment | Lifetime expected credit losses | Stage 3 | Impairment allowance      
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]      
Loans and advances £ (124)   £ (124)