Income Taxes - Additional Information (Detail) - JPY (¥) ¥ in Millions |
12 Months Ended | ||||||
|---|---|---|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2024 |
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| Income Taxes [Line Items] | |||||||
| Net operating loss carryforwards | [1],[2] | ¥ 416,000 | |||||
| Changes that directly affected Income tax expense | 5,100 | ¥ (538) | ¥ (38,055) | ||||
| Change in valuation allowance | (24,668) | (17,826) | 73,246 | ||||
| Unrecognized tax benefits, that would affect effective tax rate | 5,383 | 4,766 | 7,639 | ||||
| Unrecognized tax benefits, interest and penalties | 1,746 | ¥ 1,477 | ¥ 3,014 | ||||
| Mizuho Financial Group, Inc. | |||||||
| Income Taxes [Line Items] | |||||||
| Undistributed earnings | 580,000 | ||||||
| Deferred tax liabilities | ¥ 68,000 | ||||||
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