Investment Securities - Schedule of Fair Value of Equity Instruments Measured at Fair Value through Other Comprehensive Income at Date of Derecoginititon And Cumulative Gain on Disposal (Detail) - JPY (¥) ¥ in Millions |
12 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Disclosure of detailed information about financial instruments [abstract] | ||
| Fair value of the equity instruments at fair value through other comprehensive income at the date of derecognition | ¥ 619,772 | ¥ 667,657 |
| Cumulative gain on disposal | ¥ 482,553 | ¥ 490,955 |