v3.26.1
Pensions and other post-retirement benefits - Schedule of reconciliation of changes in the present value of defined benefit obligations (including unfunded obligations) (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of operating segments [line items]    
Opening net defined benefit asset £ 1,916  
Changes in net defined benefit liability (asset) [abstract]    
Closing net defined benefit asset 2,147 £ 1,916
Aviva    
Changes in net defined benefit liability (asset) [abstract]    
Actuarial gains (losses) arising from changes in demographic assumptions, net of tax, defined benefit plans 60  
UK | Pensions    
Disclosure of operating segments [line items]    
Opening net defined benefit asset 1,128  
Changes in net defined benefit liability (asset) [abstract]    
Closing net defined benefit asset 1,071 1,128
US | Pensions    
Disclosure of operating segments [line items]    
Opening net defined benefit asset 476  
Changes in net defined benefit liability (asset) [abstract]    
Closing net defined benefit asset 413 476
US | Other post-retirement benefits    
Disclosure of operating segments [line items]    
Opening net defined benefit asset 312  
Changes in net defined benefit liability (asset) [abstract]    
Closing net defined benefit asset 663 312
Present value of defined benefit obligation    
Disclosure of operating segments [line items]    
Opening net defined benefit asset (16,401) (17,867)
Changes in net defined benefit liability (asset) [abstract]    
Current service cost (123) (138)
Interest cost (785) (899)
Actuarial (losses)/gains – experience (133) 71
Actuarial gains/(losses) – demographic assumptions 321 (77)
Actuarial gains/(losses) – financial assumptions 27 1,181
Past service cost – augmentations and redundancies (2) (1)
Liabilities extinguished on settlements 468 0
Medicare subsidy received (37) (31)
Employee contributions (5) (5)
Benefits paid 1,147 1,203
Exchange adjustments 178 162
Closing net defined benefit asset (15,345) (16,401)
Present value of defined benefit obligation | UK | Pensions    
Disclosure of operating segments [line items]    
Opening net defined benefit asset (9,475) (10,521)
Changes in net defined benefit liability (asset) [abstract]    
Current service cost (34) (45)
Interest cost (452) (533)
Actuarial (losses)/gains – experience (40) (41)
Actuarial gains/(losses) – demographic assumptions (98) (74)
Actuarial gains/(losses) – financial assumptions 11 989
Past service cost – augmentations and redundancies (2) (1)
Liabilities extinguished on settlements 0 0
Medicare subsidy received 0 0
Employee contributions (5) (5)
Benefits paid 725 756
Exchange adjustments 0 0
Closing net defined benefit asset (9,370) (9,475)
Present value of defined benefit obligation | US | Pensions    
Disclosure of operating segments [line items]    
Opening net defined benefit asset (4,704) (4,912)
Changes in net defined benefit liability (asset) [abstract]    
Current service cost (62) (68)
Interest cost (241) (246)
Actuarial (losses)/gains – experience (88) (4)
Actuarial gains/(losses) – demographic assumptions 0 (22)
Actuarial gains/(losses) – financial assumptions 31 156
Past service cost – augmentations and redundancies 0 0
Liabilities extinguished on settlements 468 0
Medicare subsidy received 0 0
Employee contributions 0 0
Benefits paid 280 282
Exchange adjustments 121 110
Closing net defined benefit asset (4,195) (4,704)
Present value of defined benefit obligation | US | Other post-retirement benefits    
Disclosure of operating segments [line items]    
Opening net defined benefit asset (2,222) (2,434)
Changes in net defined benefit liability (asset) [abstract]    
Current service cost (27) (25)
Interest cost (92) (120)
Actuarial (losses)/gains – experience (5) 116
Actuarial gains/(losses) – demographic assumptions 419 19
Actuarial gains/(losses) – financial assumptions (15) 36
Past service cost – augmentations and redundancies 0 0
Liabilities extinguished on settlements 0 0
Medicare subsidy received (37) (31)
Employee contributions 0 0
Benefits paid 142 165
Exchange adjustments 57 52
Closing net defined benefit asset £ (1,780) £ (2,222)