v3.25.2
Fair value of financial instruments - Fair value adjustments (Details) - GBP (£)
£ in Millions
Jun. 30, 2025
Dec. 31, 2024
Exit price adjustments derived from market bid-offer spreads    
Disclosure of detailed information about financial instruments [line items]    
Fair value adjustments £ (523)  
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 (523) £ (529)
Uncollateralised derivative funding    
Disclosure of detailed information about financial instruments [line items]    
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]    
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]    
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