Employee benefits - Summary of Fair Value of Plan Assets Japanese Plans (Parenthetical) (Detail) - Japanese Defined Benefit Plans [Member] |
Mar. 31, 2025 |
|---|---|
| Defined Benefit Plan Japanese National and local Governments Debt Securities [Member] | |
| Disclosure of fair value of plan assets [line items] | |
| Defined benefit plan percentage of amount contributed to fair value of plan assets | 84.00% |
| Defined Benefit Plan Foreign National and Local Governments Debt Securities [Member] | |
| Disclosure of fair value of plan assets [line items] | |
| Defined benefit plan percentage of amount contributed to fair value of plan assets | 16.00% |