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Credit risk - Schedule of Loans and Advances by Credit Grade (Details) - GBP (£)
£ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disclosure of credit risk exposure [line items]      
Total financial assets £ 870,816 £ 846,753  
Total loans and advances to customers      
Disclosure of credit risk exposure [line items]      
Total financial assets 459,857 449,745  
Total loans and advances to customers | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 404,624 384,394  
Total loans and advances to customers | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 43,605 51,700  
Total loans and advances to customers | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,608 6,010  
Total loans and advances to customers | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,020 7,641  
Retail – UK mortgages      
Disclosure of credit risk exposure [line items]      
Total financial assets 312,280 306,215  
Retail – UK mortgages | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 269,707 256,435  
Retail – UK mortgages | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 32,722 38,159  
Retail – UK mortgages | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 3,831 3,980  
Retail – UK mortgages | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,020 7,641  
Credit cards      
Disclosure of credit risk exposure [line items]      
Total financial assets 15,661 15,118  
Credit cards | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 13,385 12,457  
Credit cards | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,144 2,507  
Credit cards | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 132 154  
Commercial Banking      
Disclosure of credit risk exposure [line items]      
Total financial assets 87,602 88,607  
Commercial Banking | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 81,272 79,342  
Commercial Banking | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 4,904 7,615  
Commercial Banking | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,426 1,650  
Gross carrying amount | Total loans and advances to customers      
Disclosure of credit risk exposure [line items]      
Total financial assets 463,048 453,462 £ 459,417
Gross carrying amount | Total loans and advances to customers | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 405,360 385,294 380,991
Gross carrying amount | Total loans and advances to customers | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 44,765 53,167 61,164
Gross carrying amount | Total loans and advances to customers | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,716 7,147 7,640
Gross carrying amount | Total loans and advances to customers | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,207 7,854 9,622
Gross carrying amount | Total Retail      
Disclosure of credit risk exposure [line items]      
Total financial assets 374,559 363,870  
Gross carrying amount | Total Retail | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 323,878 305,763  
Gross carrying amount | Total Retail | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 39,597 45,180  
Gross carrying amount | Total Retail | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 4,877 5,073  
Gross carrying amount | Total Retail | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,207 7,854  
Gross carrying amount | Retail – UK mortgages      
Disclosure of credit risk exposure [line items]      
Total financial assets 313,128 307,320 312,338
Gross carrying amount | Retail – UK mortgages | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets 282,314 230,877  
Gross carrying amount | Retail – UK mortgages | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets 15,871 56,674  
Gross carrying amount | Retail – UK mortgages | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,408 2,932  
Gross carrying amount | Retail – UK mortgages | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 290 590  
Gross carrying amount | Retail – UK mortgages | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,872 4,056  
Gross carrying amount | Retail – UK mortgages | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets 10,373 12,191  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 269,760 256,596 257,517
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 32,995 38,533 41,783
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 261,101 226,740  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 21,213 4,137  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 8,487 29,637  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 7,384 27,037  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 112 219  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,296 2,713  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 17 0  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 273 590  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 43 0  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,829 4,056  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 4,166 4,337 3,416
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 4,166 4,337  
Gross carrying amount | Retail – UK mortgages | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,207 7,854 9,622
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK mortgages | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6,207 7,854  
Gross carrying amount | Credit cards      
Disclosure of credit risk exposure [line items]      
Total financial assets 16,240 15,817 14,992
Gross carrying amount | Credit cards | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,068 3,911  
Gross carrying amount | Credit cards | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets 8,360 8,407  
Gross carrying amount | Credit cards | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,101 2,617  
Gross carrying amount | Credit cards | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 152 232  
Gross carrying amount | Credit cards | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 294 366  
Gross carrying amount | Credit cards | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets 265 284  
Gross carrying amount | Credit cards | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 13,534 12,625 11,416
Gross carrying amount | Credit cards | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,441 2,908 3,287
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,058 3,906  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 10 5  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 7,231 7,159  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,129 1,248  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,242 1,548  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 859 1,069  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 3 12  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 149 220  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 294 366  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 265 284 289
Gross carrying amount | Credit cards | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 265 284  
Gross carrying amount | Credit cards | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Credit cards | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts      
Disclosure of credit risk exposure [line items]      
Total financial assets 10,736 8,486  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,209 639  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets 7,504 5,402  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,354 1,729  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 142 178  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 352 342  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets 175 196  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 9,314 7,103  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,247 1,187  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,207 638  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2 1  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 7,020 5,152  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 484 250  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,047 1,256  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 307 473  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 31 43  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 111 135  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 9 14  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 343 328  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 175 196  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 175 196  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance      
Disclosure of credit risk exposure [line items]      
Total financial assets 16,419 15,680  
Gross carrying amount | Retail – UK Motor Finance | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets 9,727 10,548  
Gross carrying amount | Retail – UK Motor Finance | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,656 3,789  
Gross carrying amount | Retail – UK Motor Finance | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets 687 997  
Gross carrying amount | Retail – UK Motor Finance | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 46 63  
Gross carrying amount | Retail – UK Motor Finance | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 179 171  
Gross carrying amount | Retail – UK Motor Finance | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets 124 112  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 13,897 13,541  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,398 2,027  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 8,967 9,979  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 760 569  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 4,487 2,791  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,169 998  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 440 769  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 247 228  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 46 63  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 3 2  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 176 169  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 124 112  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 124 112  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – UK Motor Finance | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other      
Disclosure of credit risk exposure [line items]      
Total financial assets 18,036 16,567  
Gross carrying amount | Retail – other | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets 15,401 13,853  
Gross carrying amount | Retail – other | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,322 2,383  
Gross carrying amount | Retail – other | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets 150 86  
Gross carrying amount | Retail – other | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 7 6  
Gross carrying amount | Retail – other | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 9 95  
Gross carrying amount | Retail – other | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets 147 144  
Gross carrying amount | Retail – other | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 17,373 15,898  
Gross carrying amount | Retail – other | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 516 525  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 15,163 13,613  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 238 240  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 2,132 2,197  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 190 186  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 78 0  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 72 86  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 7 6  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 88  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 9 7  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 147 144  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 147 144  
Gross carrying amount | Retail – other | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Retail – other | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking      
Disclosure of credit risk exposure [line items]      
Total financial assets 88,484 89,629 95,373
Gross carrying amount | Commercial Banking | CMS 1–5      
Disclosure of credit risk exposure [line items]      
Total financial assets 26,931 14,107  
Gross carrying amount | Commercial Banking | CMS 6–10      
Disclosure of credit risk exposure [line items]      
Total financial assets 17,182 30,658  
Gross carrying amount | Commercial Banking | CMS 11–14      
Disclosure of credit risk exposure [line items]      
Total financial assets 33,552 34,137  
Gross carrying amount | Commercial Banking | CMS 15–18      
Disclosure of credit risk exposure [line items]      
Total financial assets 8,255 7,834  
Gross carrying amount | Commercial Banking | CMS 19      
Disclosure of credit risk exposure [line items]      
Total financial assets 725 825  
Gross carrying amount | Commercial Banking | CMS 20–23      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,839 2,068  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 81,477 79,574 80,509
Gross carrying amount | Commercial Banking | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,168 7,987 11,493
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 1–5 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 26,925 14,100  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 6 7  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 6–10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 17,126 30,534  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 56 124  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 11–14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 32,424 31,210  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,128 2,927  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 15–18 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 5,002 3,719  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 3,253 4,115  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 19 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 11  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 725 814  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 20–23 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 1 and 2 | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,839 2,068 3,371
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | Stage 3 £m | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 1,839 2,068  
Gross carrying amount | Commercial Banking | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Commercial Banking | POCI £m | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Other      
Disclosure of credit risk exposure [line items]      
Total financial assets 5 (37)  
Gross carrying amount | Other | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 5 (43)  
Gross carrying amount | Other | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Gross carrying amount | Other | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 6  
Gross carrying amount | Other | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (3,481) (4,084)  
Allowance for expected credit losses | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (889) (1,091)  
Allowance for expected credit losses | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1,286) (1,629)  
Allowance for expected credit losses | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1,119) (1,151)  
Allowance for expected credit losses | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (187) (213)  
Allowance for expected credit losses | Total loans and advances to customers      
Disclosure of credit risk exposure [line items]      
Total financial assets (3,191) (3,717) (4,518)
Allowance for expected credit losses | Total loans and advances to customers | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (736) (900) (700)
Allowance for expected credit losses | Total loans and advances to customers | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1,160) (1,467) (1,808)
Allowance for expected credit losses | Total loans and advances to customers | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1,108) (1,137) (1,757)
Allowance for expected credit losses | Total loans and advances to customers | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (187) (213) (253)
Allowance for expected credit losses | Total Retail      
Disclosure of credit risk exposure [line items]      
Total financial assets (2,309) (2,691)  
Allowance for expected credit losses | Total Retail | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (531) (668)  
Allowance for expected credit losses | Total Retail | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (896) (1,095)  
Allowance for expected credit losses | Total Retail | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (695) (715)  
Allowance for expected credit losses | Total Retail | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (187) (213)  
Allowance for expected credit losses | Retail – UK mortgages      
Disclosure of credit risk exposure [line items]      
Total financial assets (848) (1,105) (1,207)
Allowance for expected credit losses | Retail – UK mortgages | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets (189) (160)  
Allowance for expected credit losses | Retail – UK mortgages | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets (57) (189)  
Allowance for expected credit losses | Retail – UK mortgages | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets (15) (37)  
Allowance for expected credit losses | Retail – UK mortgages | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets (5) (13)  
Allowance for expected credit losses | Retail – UK mortgages | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets (60) (136)  
Allowance for expected credit losses | Retail – UK mortgages | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets (522) (570)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (53) (161) (91)
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (273) (374) (552)
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (46) (123)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (143) (37)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (6) (38)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (51) (151)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (15) (37)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (5) (13)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1) 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (59) (136)  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (335) (357) (311)
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (335) (357)  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (187) (213) (253)
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK mortgages | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (187) (213)  
Allowance for expected credit losses | Credit cards      
Disclosure of credit risk exposure [line items]      
Total financial assets (579) (699) (666)
Allowance for expected credit losses | Credit cards | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets (12) (9)  
Allowance for expected credit losses | Credit cards | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets (139) (156)  
Allowance for expected credit losses | Credit cards | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets (158) (212)  
Allowance for expected credit losses | Credit cards | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets (31) (51)  
Allowance for expected credit losses | Credit cards | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets (106) (141)  
Allowance for expected credit losses | Credit cards | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets (133) (130)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (149) (168) (120)
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (297) (401) (433)
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (11) (9)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1) 0  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (87) (91)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (52) (65)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (51) (67)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (107) (145)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 (1)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (31) (50)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (106) (141)  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (133) (130) (113)
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (133) (130)  
Allowance for expected credit losses | Credit cards | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Credit cards | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts      
Disclosure of credit risk exposure [line items]      
Total financial assets (460) (460)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (1)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets (125) (101)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets (76) (94)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets (25) (31)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets (113) (115)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets (118) (118)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (145) (134)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (197) (208)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (1)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (98) (83)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (27) (18)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (40) (44)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (36) (50)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (4)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (22) (27)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (1) (2)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (112) (113)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (118) (118)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (118) (118)  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK unsecured loans and overdrafts | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance      
Disclosure of credit risk exposure [line items]      
Total financial assets (356) (340)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets (128) (154)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets (95) (70)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets (19) (16)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets (6) (7)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets (36) (30)  
Allowance for expected credit losses | Retail – UK Motor Finance | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets (72) (63)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (169) (186)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (115) (91)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (112) (142)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (16) (12)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (55) (41)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (40) (29)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (2) (3)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (17) (13)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (6) (7)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (36) (30)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (72) (63)  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (72) (63)  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – UK Motor Finance | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other      
Disclosure of credit risk exposure [line items]      
Total financial assets (66) (87)  
Allowance for expected credit losses | Retail – other | RMS 1–3      
Disclosure of credit risk exposure [line items]      
Total financial assets (8) (7)  
Allowance for expected credit losses | Retail – other | RMS 4–6      
Disclosure of credit risk exposure [line items]      
Total financial assets (18) (29)  
Allowance for expected credit losses | Retail – other | RMS 7–9      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (4)  
Allowance for expected credit losses | Retail – other | RMS 10      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | RMS 11–13      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | RMS 14      
Disclosure of credit risk exposure [line items]      
Total financial assets (37) (47)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (15) (19)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (14) (21)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 1–3 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (4) (3)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (4) (4)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 4–6 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (11) (16)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (7) (13)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 7–9 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (4)  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 11–13 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 1 and 2 | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (37) (47)  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | Stage 3 £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (37) (47)  
Allowance for expected credit losses | Retail – other | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 1–3 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 4–6 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 7–9 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 11–13 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Retail – other | POCI £m | RMS 14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking      
Disclosure of credit risk exposure [line items]      
Total financial assets (882) (1,022) (1,698)
Allowance for expected credit losses | Commercial Banking | CMS 1–5      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (2)  
Allowance for expected credit losses | Commercial Banking | CMS 6–10      
Disclosure of credit risk exposure [line items]      
Total financial assets (13) (32)  
Allowance for expected credit losses | Commercial Banking | CMS 11–14      
Disclosure of credit risk exposure [line items]      
Total financial assets (143) (192)  
Allowance for expected credit losses | Commercial Banking | CMS 15–18      
Disclosure of credit risk exposure [line items]      
Total financial assets (233) (297)  
Allowance for expected credit losses | Commercial Banking | CMS 19      
Disclosure of credit risk exposure [line items]      
Total financial assets (77) (81)  
Allowance for expected credit losses | Commercial Banking | CMS 20–23      
Disclosure of credit risk exposure [line items]      
Total financial assets (413) (418)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (205) (232) (214)
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (264) (372) (414)
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 1–5 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (3) (2)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 6–10 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (13) (32)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 11–14 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (122) (133)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (21) (59)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 15–18 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (67) (65)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (166) (232)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 19 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (77) (81)  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 20–23 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 1 and 2 | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (413) (418) £ (1,070)
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | Stage 3 £m | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets (413) (418)  
Allowance for expected credit losses | Commercial Banking | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 1–5 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 6–10 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 11–14 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 15–18 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 19 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Commercial Banking | POCI £m | CMS 20–23 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Other      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 (4)  
Allowance for expected credit losses | Other | Stage 1 and 2 | 12-month expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Other | Stage 1 and 2 | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 0  
Allowance for expected credit losses | Other | Stage 3 £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets 0 (4)  
Allowance for expected credit losses | Other | POCI £m | Lifetime expected credit losses      
Disclosure of credit risk exposure [line items]      
Total financial assets £ 0 £ 0