v3.25.4
Retirement benefits - Disclosure of balance sheet reconciliation (Details) - GBP (£)
£ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Sep. 30, 2024
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period £ 3,099      
Current service cost (122) £ (150) £ (119)  
Interest costs or income on scheme liabilities or assets 163 157 222  
Curtailments or settlements (53) 0 0  
Net defined benefit liability (asset), end of period 3,083 3,099    
Net surplus 3,083 3,099    
Retirement benefit assets 3,240 3,263    
Retirement benefit liabilities (157) (164)    
UKRF | UK        
Reconciliation of changes in net assets available for benefits [abstract]        
Current service cost (135)      
UKRF | UK | Pension defined benefit plans        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period 3,199      
Benefits paid 1,158 1,189    
Net defined benefit liability (asset), end of period 3,181 3,199    
Net surplus 3,181 3,199   £ 1,750
Retirement benefit assets 3,181 3,199    
Retirement benefit liabilities 0 0    
Defined benefit obligations        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period (19,524) (21,420)    
Current service cost (135) (168)    
Interest costs or income on scheme liabilities or assets (1,005) (930)    
Curtailments or settlements 697 0    
Remeasurement gain - financial 541 1,804    
Remeasurement (loss)/gain - demographic (59) 12    
Remeasurement loss - experience (197) (55)    
Employee contributions (5) (6)    
Benefits paid 1,197 1,226    
Exchange and other movements 15 13    
Net defined benefit liability (asset), end of period (18,475) (19,524) (21,420)  
Defined benefit obligations | UKRF | UK        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period (18,729)      
Net defined benefit liability (asset), end of period   (18,729)    
Defined benefit obligations | UKRF | UK | Pension defined benefit plans        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period (18,729) (20,618)    
Current service cost (120) (155)    
Interest costs or income on scheme liabilities or assets (975) (901)    
Curtailments or settlements 697 0    
Remeasurement gain - financial 546 1,797    
Remeasurement (loss)/gain - demographic (47) 13    
Remeasurement loss - experience (203) (54)    
Employee contributions 0 0    
Benefits paid 1,158 1,189    
Exchange and other movements (1) 0    
Net defined benefit liability (asset), end of period (17,674) (18,729) (20,618)  
Fair value of plan assets        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period 22,623 24,914    
Interest costs or income on scheme liabilities or assets 1,168 1,087    
Employer contribution 29 37    
Settlements (750) 0    
Remeasurement - return on scheme assets less than discount rate (299) (2,192)    
Employee contributions 5 6    
Benefits paid (1,189) (1,221)    
Exchange and other movements (29) (8)    
Net defined benefit liability (asset), end of period 21,558 22,623 24,914  
Fair value of plan assets | UKRF | UK | Pension defined benefit plans        
Reconciliation of changes in net assets available for benefits [abstract]        
Net defined benefit liability (asset), beginning of period 21,928 24,234    
Interest costs or income on scheme liabilities or assets 1,143 1,062    
Employer contribution 16 22    
Settlements (750) 0    
Remeasurement - return on scheme assets less than discount rate (310) (2,184)    
Employee contributions 0 0    
Benefits paid (1,158) (1,189)    
Exchange and other movements (14) (17)    
Net defined benefit liability (asset), end of period £ 20,855 £ 21,928 £ 24,234