v3.26.1
Credit risk - Disclosure of management adjustments to models for impairment (Details) - GBP (£)
£ in Millions
Jun. 30, 2026
Dec. 31, 2025
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance 3.20% 4.90%
Total loans and advances at amortised cost    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance 3.20% 4.90%
Total loans and advances at amortised cost | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance   2.10%
Retail credit cards    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance 2.00% 4.50%
Retail credit cards | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance   2.10%
Corporate loans    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance 5.40% 5.50%
Corporate loans | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Proportion of Management adjustments to total impairment allowance   0.00%
Impairment allowance | Total impairment allowance    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets £ 4,230 £ 4,034
Impairment allowance | Impairment allowance pre management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 4,094 3,835
Impairment allowance | Management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 136 199
Impairment allowance | Economic uncertainty adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 66 81
Impairment allowance | Other adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 70 118
Impairment allowance | Total loans and advances at amortised cost | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   236
Impairment allowance | Total loans and advances at amortised cost | Total impairment allowance    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 4,214 4,015
Impairment allowance | Total loans and advances at amortised cost | Total impairment allowance | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   240
Impairment allowance | Total loans and advances at amortised cost | Impairment allowance pre management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 4,080 3,817
Impairment allowance | Total loans and advances at amortised cost | Impairment allowance pre management adjustments | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   235
Impairment allowance | Total loans and advances at amortised cost | Management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 134 198
Impairment allowance | Total loans and advances at amortised cost | Management adjustments | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   5
Impairment allowance | Total loans and advances at amortised cost | Economic uncertainty adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 64 80
Impairment allowance | Total loans and advances at amortised cost | Economic uncertainty adjustments | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   5
Impairment allowance | Total loans and advances at amortised cost | Other adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 70 118
Impairment allowance | Total loans and advances at amortised cost | Other adjustments | Assets classified as held for sale    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   0
Impairment allowance | Retail credit cards    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 2,647 2,586
Impairment allowance | Retail credit cards | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   233
Impairment allowance | Retail credit cards | Total impairment allowance    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 2,690 2,623
Impairment allowance | Retail credit cards | Total impairment allowance | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   237
Impairment allowance | Retail credit cards | Impairment allowance pre management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 2,635 2,505
Impairment allowance | Retail credit cards | Impairment allowance pre management adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   232
Impairment allowance | Retail credit cards | Management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 55 118
Impairment allowance | Retail credit cards | Management adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   5
Impairment allowance | Retail credit cards | Economic uncertainty adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 0 31
Impairment allowance | Retail credit cards | Economic uncertainty adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   5
Impairment allowance | Retail credit cards | Other adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 55 87
Impairment allowance | Retail credit cards | Other adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   0
Impairment allowance | Corporate loans    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 1,088 966
Impairment allowance | Corporate loans | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   3
Impairment allowance | Corporate loans | Total impairment allowance    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 1,454 1,326
Impairment allowance | Corporate loans | Total impairment allowance | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   3
Impairment allowance | Corporate loans | Impairment allowance pre management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 1,376 1,253
Impairment allowance | Corporate loans | Impairment allowance pre management adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   3
Impairment allowance | Corporate loans | Management adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 78 73
Impairment allowance | Corporate loans | Management adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   0
Impairment allowance | Corporate loans | Economic uncertainty adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets 64 49
Impairment allowance | Corporate loans | Economic uncertainty adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   0
Impairment allowance | Corporate loans | Other adjustments    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets £ 14 24
Impairment allowance | Corporate loans | Other adjustments | Assets classified as held for sale | American Airlines Portfolio    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Financial assets   £ 0