Investment Securities (Net Realized Gains (Losses) on Sales of Equity Securities and Net Unrealized Gains (Losses) on Equity Securities still held) (Detail) - JPY (¥) ¥ in Millions |
12 Months Ended | ||
|---|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
Mar. 31, 2023 |
|
| Investments, Debt and Equity Securities [Abstract] | |||
| Net gains (losses) recognized during the period | ¥ (674,282) | ¥ 1,527,792 | ¥ 102,415 |
| Net gains (losses) recognized during the period on equity securities sold during the period | (107,892) | 113,216 | 18,228 |
| Net unrealized gains (losses) recognized during the reporting period still held at the reporting date | ¥ (566,390) | ¥ 1,414,576 | ¥ 84,187 |