v3.25.4
Derivative financial instruments - Disclosure of hedged items in cash flow hedges and hedges of net investments in foreign operations (Details) - GBP (£)
£ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of detailed information about hedged items [line items]      
Balance in currency translation reserve for continuing hedges £ 2,534 £ 3,690 £ 3,783
Cash flow hedges      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (2,630) 1,369  
Balance in cash flow hedging reserve for continuing hedges (248) 329  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 1,501 3,072  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (2,630) 1,369  
Hedge ineffectiveness recognised in the income statement 12 19  
Cash flow hedges | Cash and balances at central banks | Interest rate risk      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (553) 495  
Balance in cash flow hedging reserve for continuing hedges (149) 123  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 604 1,495  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (553) 495  
Hedge ineffectiveness recognised in the income statement (19) 22  
Cash flow hedges | Subordinated liabilities | Foreign exchange risk      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness 9 18  
Balance in cash flow hedging reserve for continuing hedges 16 (9)  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income 9 18  
Hedge ineffectiveness recognised in the income statement 0 0  
Hedge of net investment in foreign operations      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (499) 10  
Balance in cash flow hedging reserve for continuing hedges 0 0  
Balance in currency translation reserve for continuing hedges 1,148 1,457  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 60 96  
Hedging gains or losses recognised in other comprehensive income (499) 10  
Hedge ineffectiveness recognised in the income statement 0 0  
Hedge of net investment in foreign operations | USD foreign operations      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (484) 136  
Balance in cash flow hedging reserve for continuing hedges 0 0  
Balance in currency translation reserve for continuing hedges 1,151 1,449  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (484) 136  
Hedge ineffectiveness recognised in the income statement 0 0  
Hedge of net investment in foreign operations | EUR foreign operations      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness 146 (109)  
Balance in cash flow hedging reserve for continuing hedges 0 0  
Balance in currency translation reserve for continuing hedges 100 (26)  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income 146 (109)  
Hedge ineffectiveness recognised in the income statement 0 0  
Hedge of net investment in foreign operations | Other foreign operations      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (161) (17)  
Balance in cash flow hedging reserve for continuing hedges 0 0  
Balance in currency translation reserve for continuing hedges (103) 34  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 60 96  
Hedging gains or losses recognised in other comprehensive income (161) (17)  
Hedge ineffectiveness recognised in the income statement 0 0  
Financial assets at amortised cost | Cash flow hedges | Loans and advances at amortised cost | Interest rate risk      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (336) 438  
Balance in cash flow hedging reserve for continuing hedges (92) 182  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 918 1,552  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (336) 438  
Hedge ineffectiveness recognised in the income statement 6 (8)  
Financial assets at amortised cost | Cash flow hedges | Loans and advances at amortised cost | Foreign exchange risk      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (1,637) 300  
Balance in cash flow hedging reserve for continuing hedges 120 106  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied 0 0  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (1,637) 300  
Hedge ineffectiveness recognised in the income statement 17 5  
Financial assets at amortised cost | Cash flow hedges | Debt securities at amortised cost | Inflation risk      
Disclosure of detailed information about hedged items [line items]      
Change in fair value used as a basis to determine ineffectiveness (113) 118  
Balance in cash flow hedging reserve for continuing hedges (143) (73)  
Balance in currency translation reserve for continuing hedges 0 0  
Balances remaining in cash flow hedging reserve for which hedge accounting is no longer applied (21) 25  
Balances remaining in currency translation reserve for which hedge accounting is no longer applied 0 0  
Hedging gains or losses recognised in other comprehensive income (113) 118  
Hedge ineffectiveness recognised in the income statement £ 8 £ 0