Income Taxes - Changes in valuation allowance for deferred tax assets (Detail) - JPY (¥) ¥ in Millions |
12 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2024 |
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| Income Tax Disclosure [Abstract] | ||||||||||||
| Balance at beginning of year | ¥ 571,017 | ¥ 595,668 | ¥ 515,068 | |||||||||
| Net change during the year | 17,409 | [1] | (24,651) | [2] | 80,600 | [3] | ||||||
| Balance at end of year | ¥ 588,426 | ¥ 571,017 | ¥ 595,668 | |||||||||
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