Retirement Benefit and Other Post-retirement Obligations - Summary of Effect Percentage of Discount Rate Increase (Decrease) on Defined Benefit Obligation and Total Pension Expense (Parenthetical) (Detail) - Rate used to discount plan liabilities [member] |
Dec. 31, 2025 |
|---|---|
| Disclosure of sensitivity analysis for actuarial assumptions [line items] | |
| Percentage movement in discount rate sensitivity analysis | 1.00% |
| Percentage movement in discount rate sensitivity analysis | 1.00% |