Fair value measurements - Equity securities subject to contractual sale restrictions (Detail) - JPY (¥) ¥ in Millions |
Mar. 31, 2026 |
Mar. 31, 2025 |
|---|---|---|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Restriction on transfer | ¥ 250,291 | ¥ 200,658 |
| Consent from third parties | 8,054 | 7,806 |
| Others | 3,745 | 2,148 |
| Total | 262,090 | 210,612 |
| Less than 1 year [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Restriction on transfer | 250,291 | 9 |
| Consent from third parties | 18 | |
| Others | ||
| Total | 250,291 | 27 |
| 1 to 5 years [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Restriction on transfer | 200,621 | |
| Consent from third parties | ||
| Others | ||
| Total | 200,621 | |
| More than 5 years [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Restriction on transfer | 28 | |
| Consent from third parties | 8,054 | 7,788 |
| Others | 3,745 | 2,148 |
| Total | ¥ 11,799 | ¥ 9,964 |