Retirement Benefit and Other Post-retirement Obligations - Summary of Effect of a Half Percentage Point Increase and Decrease in the Inflation Rate (Parenthetical) (Detail) - Inflation [member] |
Dec. 31, 2025 |
|---|---|
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| Movement in inflation sensitivity analysis | 0.50% |
| Movement in inflation sensitivity analysis | 0.50% |