Employee benefits - Summary of Fair Value of Plan Assets Japanese Plans (Parenthetical) (Detail) - Japanese Defined Benefit Plans [Member] |
Mar. 31, 2025 |
Mar. 31, 2024 |
|---|---|---|
| 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% | 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% | 16.00% |