v3.25.4
Risk Management - Disclosure of ECL under 100% weighted scenarios for key modelled portfolios (Details) - GBP (£)
£ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 1,232,975 £ 1,204,773  
Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (4,034) (3,860)  
Loans and advances at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 150,786 144,827  
Loans and advances at amortised cost | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 150,786 £ 144,827  
Coverage ratio 2.30% 2.30%  
Loans and advances at amortised cost | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 138,340 £ 132,198  
Coverage ratio 0.40% 0.40%  
Loans and advances at amortised cost | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 10,057 £ 10,591  
Coverage ratio 9.30% 9.10%  
Loans and advances at amortised cost | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 2,389 £ 2,038  
Coverage ratio 45.90% 47.80%  
Loans and advances at amortised cost | Gross exposure | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 154,403 £ 148,247  
Loans and advances at amortised cost | Gross exposure | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 138,892 132,689  
Loans and advances at amortised cost | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 138,892 132,689  
Loans and advances at amortised cost | Gross exposure | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 11,093 11,654  
Loans and advances at amortised cost | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 11,093 11,654  
Loans and advances at amortised cost | Gross exposure | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,418 3,904  
Loans and advances at amortised cost | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,418 3,904  
Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (3,617) (3,420)  
Loans and advances at amortised cost | Accumulated impairment | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (552) (491)  
Loans and advances at amortised cost | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (552) (491)  
Loans and advances at amortised cost | Accumulated impairment | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,036) (1,063)  
Loans and advances at amortised cost | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,036) (1,063)  
Loans and advances at amortised cost | Accumulated impairment | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,029) (1,866)  
Loans and advances at amortised cost | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,029) (1,866)  
Retail mortgages      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,952 4,956  
Retail mortgages | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 4,952 £ 4,956  
Coverage ratio 0.70% 0.80%  
Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 4,665 £ 4,529  
Coverage ratio 0.20% 0.20%  
Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 136 £ 149  
Coverage ratio 0.00% 0.70%  
Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 151 £ 278  
Coverage ratio 13.70% 10.30%  
Retail mortgages | Gross exposure      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 4,985 £ 4,997 £ 8,362
Retail mortgages | Gross exposure | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,985 4,997  
Retail mortgages | Gross exposure | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,674 4,537 7,257
Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,674 4,537  
Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 136 150 389
Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 136 150  
Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 175 310 716
Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 175 310  
Retail mortgages | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (33) (41) (360)
Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (33) (41)  
Retail mortgages | Accumulated impairment | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (9) (8) (11)
Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (9) (8)  
Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 (1) (28)
Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 (1)  
Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (24) (32) (321)
Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (24) (32)  
Retail credit cards      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 20,527 19,749  
Retail credit cards | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 20,527 £ 19,749  
Coverage ratio 11.20% 11.50%  
Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 18,406 £ 17,295  
Coverage ratio 2.10% 1.90%  
Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 1,740 £ 2,146  
Coverage ratio 31.40% 27.30%  
Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 381 £ 308  
Coverage ratio 78.50% 82.10%  
Retail credit cards | Gross exposure      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 23,113 £ 22,306 27,287
Retail credit cards | Gross exposure | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 23,113 22,306  
Retail credit cards | Gross exposure | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 18,801 17,629 22,315
Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 18,801 17,629  
Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 2,536 2,953 3,450
Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 2,536 2,953  
Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,776 1,724 1,522
Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,776 1,724  
Retail credit cards | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,586) (2,557) (2,776)
Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,586) (2,557)  
Retail credit cards | Accumulated impairment | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (395) (334) (412)
Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (395) (334)  
Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (796) (807) (1,138)
Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (796) (807)  
Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,395) (1,416) (1,226)
Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,395) (1,416)  
Retail other      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,128 3,918  
Retail other | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 4,128 £ 3,918  
Coverage ratio 0.80% 0.80%  
Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 3,781 £ 3,324  
Coverage ratio 0.20% 0.20%  
Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 260 £ 403  
Coverage ratio 1.90% 0.20%  
Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 87 £ 191  
Coverage ratio 18.70% 11.60%  
Retail other | Gross exposure      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 4,160 £ 3,949 3,411
Retail other | Gross exposure | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 4,160 3,949  
Retail other | Gross exposure | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,788 3,329 2,734
Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,788 3,329  
Retail other | Gross exposure | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 265 404 369
Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 265 404  
Retail other | Gross exposure | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 107 216 308
Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 107 216  
Retail other | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (32) (31) (45)
Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (32) (31)  
Retail other | Accumulated impairment | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (7) (5) (8)
Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (7) (5)  
Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (5) (1) (2)
Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (5) (1)  
Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (20) (25) (35)
Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (20) (25)  
Corporate loans      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 121,179 116,204  
Corporate loans | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 121,179 £ 116,204  
Coverage ratio 0.80% 0.70%  
Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 111,488 £ 107,050  
Coverage ratio 0.10% 0.10%  
Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 7,921 £ 7,893  
Coverage ratio 2.90% 3.10%  
Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 1,770 £ 1,261  
Coverage ratio 25.00% 23.80%  
Corporate loans | Gross exposure      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 122,145 £ 116,995 111,158
Corporate loans | Gross exposure | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 122,145 116,995  
Corporate loans | Gross exposure | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 111,629 107,194 100,956
Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 111,629 107,194  
Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 8,156 8,147 8,967
Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 8,156 8,147  
Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 2,360 1,654 1,235
Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 2,360 1,654  
Corporate loans | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (966) (791) (836)
Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (966) (791)  
Corporate loans | Accumulated impairment | Stage 1      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (141) (144) (179)
Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (141) (144)  
Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (235) (254) (309)
Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (235) (254)  
Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (590) (393) £ (348)
Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (590) (393)  
Total weighted model ECL | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (3,451) (3,712)  
Total weighted model ECL | Loans and advances at amortised cost | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (3,400) (3,700)  
Total weighted model ECL | Weighted | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (3,451) £ (3,712)  
Total weighted model ECL | Weighted | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Weighted | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Weighted | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 13.30% 20.00%  
Total weighted model ECL | Weighted | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Weighted | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Weighted | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Weighted | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2) (5)  
Total weighted model ECL | Weighted | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (2) £ (5)  
Total weighted model ECL | Weighted | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.10% 0.90%  
Total weighted model ECL | Weighted | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 24.80% 22.30%  
Total weighted model ECL | Weighted | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 75.80% 76.60%  
Total weighted model ECL | Weighted | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 41,195 £ 45,377  
Total weighted model ECL | Weighted | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,513 4,591  
Total weighted model ECL | Weighted | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Weighted | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,817) (2,981)  
Total weighted model ECL | Weighted | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (448) (422)  
Total weighted model ECL | Weighted | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (871) (1,024)  
Total weighted model ECL | Weighted | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,498) £ (1,535)  
Total weighted model ECL | Weighted | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Weighted | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Weighted | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Weighted | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Weighted | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Weighted | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Weighted | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.10%  
Total weighted model ECL | Weighted | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 2.70% 2.60%  
Total weighted model ECL | Weighted | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Weighted | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 201,622 £ 193,873  
Total weighted model ECL | Weighted | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15,180 17,769  
Total weighted model ECL | Weighted | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Weighted | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (632) (726)  
Total weighted model ECL | Weighted | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (197) (237)  
Total weighted model ECL | Weighted | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (410) (464)  
Total weighted model ECL | Weighted | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
Total weighted model ECL | Upside 2 | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (3,213) £ (3,490)  
Total weighted model ECL | Upside 2 | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 2 | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 2 | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 6.70% 16.00%  
Total weighted model ECL | Upside 2 | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Upside 2 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Upside 2 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Upside 2 | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1) (4)  
Total weighted model ECL | Upside 2 | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1) £ (4)  
Total weighted model ECL | Upside 2 | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.00% 0.90%  
Total weighted model ECL | Upside 2 | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 23.90% 21.60%  
Total weighted model ECL | Upside 2 | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 73.70% 74.60%  
Total weighted model ECL | Upside 2 | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 40,997 £ 45,328  
Total weighted model ECL | Upside 2 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,392 4,516  
Total weighted model ECL | Upside 2 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Upside 2 | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,684) (2,882)  
Total weighted model ECL | Upside 2 | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (420) (410)  
Total weighted model ECL | Upside 2 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (809) (976)  
Total weighted model ECL | Upside 2 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,455) £ (1,496)  
Total weighted model ECL | Upside 2 | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 2 | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 2 | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 2 | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Upside 2 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 2 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Upside 2 | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.10%  
Total weighted model ECL | Upside 2 | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 2.30% 2.20%  
Total weighted model ECL | Upside 2 | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Upside 2 | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 202,562 £ 194,752  
Total weighted model ECL | Upside 2 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 14,097 16,740  
Total weighted model ECL | Upside 2 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Upside 2 | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (528) (604)  
Total weighted model ECL | Upside 2 | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (172) (206)  
Total weighted model ECL | Upside 2 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (331) (373)  
Total weighted model ECL | Upside 2 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
Total weighted model ECL | Upside 1 | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (3,315) £ (3,582)  
Total weighted model ECL | Upside 1 | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 1 | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 1 | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 6.70% 20.00%  
Total weighted model ECL | Upside 1 | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Upside 1 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Upside 1 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Upside 1 | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1) (5)  
Total weighted model ECL | Upside 1 | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1) £ (5)  
Total weighted model ECL | Upside 1 | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.10% 0.90%  
Total weighted model ECL | Upside 1 | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 24.30% 21.90%  
Total weighted model ECL | Upside 1 | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 74.90% 75.70%  
Total weighted model ECL | Upside 1 | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 41,089 £ 45,352  
Total weighted model ECL | Upside 1 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,455 4,554  
Total weighted model ECL | Upside 1 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Upside 1 | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,753) (2,933)  
Total weighted model ECL | Upside 1 | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (434) (417)  
Total weighted model ECL | Upside 1 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (840) (999)  
Total weighted model ECL | Upside 1 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,479) £ (1,517)  
Total weighted model ECL | Upside 1 | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 1 | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 1 | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Upside 1 | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Upside 1 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Upside 1 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Upside 1 | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.10%  
Total weighted model ECL | Upside 1 | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 2.50% 2.40%  
Total weighted model ECL | Upside 1 | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Upside 1 | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 202,203 £ 194,413  
Total weighted model ECL | Upside 1 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 14,510 17,134  
Total weighted model ECL | Upside 1 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Upside 1 | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (561) (644)  
Total weighted model ECL | Upside 1 | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (180) (215)  
Total weighted model ECL | Upside 1 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (356) (404)  
Total weighted model ECL | Upside 1 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
Total weighted model ECL | Baseline | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (3,423) £ (3,678)  
Total weighted model ECL | Baseline | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Baseline | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Baseline | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 13.30% 20.00%  
Total weighted model ECL | Baseline | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Baseline | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Baseline | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Baseline | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2) (5)  
Total weighted model ECL | Baseline | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (2) £ (5)  
Total weighted model ECL | Baseline | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.10% 0.90%  
Total weighted model ECL | Baseline | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 24.80% 22.30%  
Total weighted model ECL | Baseline | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 76.10% 76.70%  
Total weighted model ECL | Baseline | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 41,197 £ 45,377  
Total weighted model ECL | Baseline | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,504 4,590  
Total weighted model ECL | Baseline | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Baseline | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,821) (2,983)  
Total weighted model ECL | Baseline | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (450) (423)  
Total weighted model ECL | Baseline | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (868) (1,023)  
Total weighted model ECL | Baseline | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,503) £ (1,537)  
Total weighted model ECL | Baseline | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Baseline | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Baseline | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Baseline | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Baseline | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Baseline | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Baseline | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.10%  
Total weighted model ECL | Baseline | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 2.60% 2.50%  
Total weighted model ECL | Baseline | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Baseline | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 201,950 £ 194,151  
Total weighted model ECL | Baseline | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 14,869 17,508  
Total weighted model ECL | Baseline | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Baseline | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (600) (690)  
Total weighted model ECL | Baseline | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (188) (226)  
Total weighted model ECL | Baseline | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (387) (439)  
Total weighted model ECL | Baseline | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
Total weighted model ECL | Downside 1 | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (3,726) £ (3,942)  
Total weighted model ECL | Downside 1 | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 1 | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 1 | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 13.30% 20.00%  
Total weighted model ECL | Downside 1 | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Downside 1 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Downside 1 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Downside 1 | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2) (5)  
Total weighted model ECL | Downside 1 | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (2) £ (5)  
Total weighted model ECL | Downside 1 | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.10% 0.90%  
Total weighted model ECL | Downside 1 | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 25.80% 23.00%  
Total weighted model ECL | Downside 1 | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 77.70% 78.30%  
Total weighted model ECL | Downside 1 | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 41,419 £ 45,429  
Total weighted model ECL | Downside 1 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,634 4,660  
Total weighted model ECL | Downside 1 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Downside 1 | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2,945) (3,071)  
Total weighted model ECL | Downside 1 | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (475) (431)  
Total weighted model ECL | Downside 1 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (936) (1,070)  
Total weighted model ECL | Downside 1 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,534) £ (1,570)  
Total weighted model ECL | Downside 1 | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 1 | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 1 | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 1 | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Downside 1 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 1 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Downside 1 | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.10%  
Total weighted model ECL | Downside 1 | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 3.20% 3.10%  
Total weighted model ECL | Downside 1 | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Downside 1 | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 200,869 £ 193,208  
Total weighted model ECL | Downside 1 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 16,082 18,576  
Total weighted model ECL | Downside 1 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Downside 1 | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (779) (866)  
Total weighted model ECL | Downside 1 | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (233) (272)  
Total weighted model ECL | Downside 1 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (521) (569)  
Total weighted model ECL | Downside 1 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
Total weighted model ECL | Downside 2 | Loans and advances at amortised cost | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (4,170) £ (4,324)  
Total weighted model ECL | Downside 2 | Retail mortgages | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 2 | Retail mortgages | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 2 | Retail mortgages | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 13.30% 20.00%  
Total weighted model ECL | Downside 2 | Retail mortgages | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 13 £ 9  
Total weighted model ECL | Downside 2 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1 3  
Total weighted model ECL | Downside 2 | Retail mortgages | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 15 25  
Total weighted model ECL | Downside 2 | Retail mortgages | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (2) (5)  
Total weighted model ECL | Downside 2 | Retail mortgages | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail mortgages | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (2) £ (5)  
Total weighted model ECL | Downside 2 | Retail credit cards | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 1.20% 1.00%  
Total weighted model ECL | Downside 2 | Retail credit cards | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 26.80% 23.70%  
Total weighted model ECL | Downside 2 | Retail credit cards | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 79.10% 79.70%  
Total weighted model ECL | Downside 2 | Retail credit cards | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 41,583 £ 45,462  
Total weighted model ECL | Downside 2 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 3,837 4,752  
Total weighted model ECL | Downside 2 | Retail credit cards | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 1,975 2,005  
Total weighted model ECL | Downside 2 | Retail credit cards | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (3,092) (3,163)  
Total weighted model ECL | Downside 2 | Retail credit cards | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (500) (438)  
Total weighted model ECL | Downside 2 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,029) (1,127)  
Total weighted model ECL | Downside 2 | Retail credit cards | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (1,563) £ (1,598)  
Total weighted model ECL | Downside 2 | Retail other | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 2 | Retail other | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 2 | Retail other | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.00% 0.00%  
Total weighted model ECL | Downside 2 | Retail other | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Downside 2 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail other | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail other | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail other | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 0 0  
Total weighted model ECL | Downside 2 | Retail other | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 0 £ 0  
Total weighted model ECL | Downside 2 | Corporate loans | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 0.10% 0.20%  
Total weighted model ECL | Downside 2 | Corporate loans | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 3.90% 3.70%  
Total weighted model ECL | Downside 2 | Corporate loans | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Coverage ratio 71.40% 73.50%  
Total weighted model ECL | Downside 2 | Corporate loans | Gross exposure | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ 197,068 £ 189,985  
Total weighted model ECL | Downside 2 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 20,024 21,956  
Total weighted model ECL | Downside 2 | Corporate loans | Gross exposure | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 35 34  
Total weighted model ECL | Downside 2 | Corporate loans | Accumulated impairment | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (1,076) (1,156)  
Total weighted model ECL | Downside 2 | Corporate loans | Accumulated impairment | Stage 1 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (280) (318)  
Total weighted model ECL | Downside 2 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 2 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (771) (813)  
Total weighted model ECL | Downside 2 | Corporate loans | Accumulated impairment | Lifetime expected credit losses | Stage 3 | Financial assets at amortised cost      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (25) (25)  
ECL from individually assessed exposures | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (538) (329)  
ECL from individually assessed exposures | Loans and advances at amortised cost | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (500) (300)  
ECL from benchmarked exposures and others | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (63) (103)  
ECL from benchmarked exposures and others | Loans and advances at amortised cost | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (100) (100)  
ECL from debt securities at amortised cost | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (19) (20)  
ECL from held for sale assets (co-branded card portfolio) | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances 235 282  
ECL from post model management adjustments | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances (198) 22  
ECL from economic uncertainty adjustments | Accumulated impairment      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Loans and advances £ (80) £ 0