v3.25.4
Retirement Benefit and Other Post-retirement Obligations - Summary of Gains (Losses) Recognised in Other Comprehensive Income (Detail) - GBP (£)
£ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of defined benefit plans gain loss recognised [line items]      
Gains (losses) recognised for benefit plans £ 10 £ 5 £ (85)
Defined benefit plan [member]      
Disclosure of defined benefit plans gain loss recognised [line items]      
Gains (losses) recognised for benefit plans 11 4 (86)
PRMB [member]      
Disclosure of defined benefit plans gain loss recognised [line items]      
Gains (losses) recognised for benefit plans £ (1) £ 1 £ 1