Employee retirement benefits - Assumptions Used to Determine Net Periodic Benefit (Detail) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Schedule Of Defined Benefit Plans Disclosures [Line Items] | |||
| Long-term rate of return on funded assets | 4.40% | ||
| Pension benefits | |||
| Schedule Of Defined Benefit Plans Disclosures [Line Items] | |||
| Discount rate | 4.70% | 4.60% | 5.10% |
| Long-term rate of return on funded assets | 4.40% | 5.60% | 4.80% |
| Long-term rate of compensation increase | 4.00% | 4.00% | 4.00% |
| Other postretirement benefits | |||
| Schedule Of Defined Benefit Plans Disclosures [Line Items] | |||
| Discount rate | 4.70% | 4.60% | 5.10% |
| Long-term rate of return on funded assets | 0.00% | 0.00% | 0.00% |
| Long-term rate of compensation increase | 4.00% | 4.00% | 4.00% |