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
Significant unobservable inputs (Level 3) | Favourable changes    
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) £ 1,188 £ 1,512
Decrease in fair value measurement due to change in one or more unobservable inputs to reflect reasonably possible alternative assumptions, assets (liabilities) 1,249 1,782
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 (536)  
Exit price adjustments derived from market bid-offer spreads | Significant unobservable inputs (Level 3)    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments (536) (542)
Uncollateralised derivative funding    
Disclosure of detailed information about financial instruments [line items]    
Increase (decrease) in derivative fair value adjustments 9  
Fair value adjustments 28  
Uncollateralised derivative funding | Significant unobservable inputs (Level 3)    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments 28 19
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 credit valuation adjustments | Significant unobservable inputs (Level 3)    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments (189) (184)
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  
Derivative debit valuation adjustments | Significant unobservable inputs (Level 3)    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments 117 108
Brokered certificates of deposit    
Disclosure of detailed information about financial instruments [line items]    
Deposits at amortised cost 3,004 4,844
Financial instruments at fair value, category | Significant unobservable inputs (Level 3)    
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 266 273
Additions, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 47 173
Amortisation and releases, aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss 54 105
Financial instruments at amortised cost, category | Significant unobservable inputs (Level 3)    
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 168 173
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 £ 5 £ 19