Fair Value (Losses (Gains) Recorded as a Result of Changes in Fair Value Measured on a Nonrecurring Basis) (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	¥ 202,255	¥ 257,606
Investment securities
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	10,411	29,409
Loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	56,678	23,210
Loans \| Loans held for sale
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	4,075	6,903
Loans \| Collateral dependent loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	52,603	16,307
Premises and equipment
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	3,290	14,490
Intangible assets
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	5,658	13,057
Goodwill
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	97,475	150,089
Other assets
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	28,743	27,351
Other assets \| Investments in equity method investees
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	6,306	8,177
Other assets \| Other
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Losses (gains) on change in fair value	¥ 22,437	¥ 19,174