Fair value measurements - Geographic allocations of trading assets related to government, agency and municipal securities (Detail) - Government, agency and municipal securities [Member] - JPY (¥) ¥ in Billions |
Mar. 31, 2026 |
Mar. 31, 2025 |
|---|---|---|
| Fair value, concentration of credit risk [Line items] | ||
| Trading assets | ¥ 11,269 | ¥ 9,650 |
| Japan [Member] | ||
| Fair value, concentration of credit risk [Line items] | ||
| Trading assets | 4,125 | 2,896 |
| U.S. [Member] | ||
| Fair value, concentration of credit risk [Line items] | ||
| Trading assets | 3,141 | 2,629 |
| EU & U.K. [Member] | ||
| Fair value, concentration of credit risk [Line items] | ||
| Trading assets | 2,587 | 2,655 |
| Other [Member] | ||
| Fair value, concentration of credit risk [Line items] | ||
| Trading assets | ¥ 1,416 | ¥ 1,470 |