Retirement Benefit and Other Post-retirement Obligations - Summary of Effect of a Half Percentage Point Increase and Decrease in the Inflation Rate (Detail) - Inflation [member] £ in Millions |
Dec. 31, 2025
GBP (£)
|
|---|---|
| UK Group plan [member] | |
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| (Decrease) /increase in defined benefit obligation, 0.5% increase | £ 38 |
| (Decrease) /increase in defined benefit obligation, 0.5% decrease | (36) |
| US plan [member] | |
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| (Decrease) /increase in defined benefit obligation, 0.5% increase | 0 |
| (Decrease) /increase in defined benefit obligation, 0.5% decrease | £ 0 |