Retirement Benefit and Other Post-retirement Obligations - Summary of Effect of Members Living One Year More or One Year Less on the Defined Benefit Obligation (Detail) - Actuarial Assumption of Longevity [member] £ in Millions |
Dec. 31, 2025
GBP (£)
|
|---|---|
| UK Group plan [member] | |
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| Increase/(decrease) in defined benefit obligation, 1 year increase | £ 40 |
| Increase/(decrease) in defined benefit obligation, 1 year decrease | (39) |
| US defined benefit pension plans [member] | |
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| Increase/(decrease) in defined benefit obligation, 1 year increase | 0 |
| Increase/(decrease) in defined benefit obligation, 1 year decrease | £ 0 |