v3.25.2
Fair value of financial instruments - Narrative (Details) - GBP (£)
£ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2025
Dec. 31, 2024
Brokered certificates of deposit    
Disclosure of detailed information about financial instruments [line items]    
Deposits at amortised cost £ 3,004 £ 4,844
Exit price adjustments derived from market bid-offer spreads    
Disclosure of detailed information about financial instruments [line items]    
Increase (decrease) in derivative fair value adjustments (6)  
Fair value adjustments (523)  
Uncollateralised derivative funding    
Disclosure of detailed information about financial instruments [line items]    
Increase (decrease) in derivative fair value adjustments 9  
Fair value adjustments 28  
Derivative credit valuation adjustments    
Disclosure of detailed information about financial instruments [line items]    
Increase (decrease) in derivative fair value adjustments 5  
Fair value adjustments (189)  
Derivative debit valuation adjustments    
Disclosure of detailed information about financial instruments [line items]    
Increase (decrease) in derivative fair value adjustments 9  
Fair value adjustments 117  
Significant unobservable inputs (Level 3) | Exit price adjustments derived from market bid-offer spreads    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments (523) (529)
Significant unobservable inputs (Level 3) | Uncollateralised derivative funding    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments 28 19
Significant unobservable inputs (Level 3) | Derivative credit valuation adjustments    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments (189) (184)
Significant unobservable inputs (Level 3) | Derivative debit valuation adjustments    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments 117 108
Significant unobservable inputs (Level 3) | Financial instruments at fair value, category    
Disclosure of detailed information about financial instruments [line items]    
Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 260 267
Additions, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 47 177
Amortisation and releases, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 54 104
Significant unobservable inputs (Level 3) | Financial instruments at amortised cost, category    
Disclosure of detailed information about financial instruments [line items]    
Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 16 17
Additions, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 0 0
Amortisation and releases, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 1 1
Significant unobservable inputs (Level 3) | Top of range    
Disclosure of detailed information about financial instruments [line items]    
Increase in fair value measurement due to change in one or more unobservable inputs to reflect reasonably possible alternative assumptions, assets (liabilities) 936 1,231
Decrease in fair value measurement due to change in one or more unobservable inputs to reflect reasonably possible alternative assumptions, assets (liabilities) £ 1,017 £ 1,554