Loans and Allowance for Credit Losses (Financial Effect of Modifications) (Details) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Commercial \| Domestic
Financing Receivable, Modifications [Line Items]
Weighted average interest rate decrease from modification	0.11%	0.11%	0.13%
Weighted average term increase from modificationn	1 year 1 month 6 days	9 months 18 days	1 year
Commercial \| Foreign
Financing Receivable, Modifications [Line Items]
Weighted average interest rate decrease from modification	0.68%		0.46%
Weighted average term increase from modificationn	1 year	8 months 12 days	9 months 18 days
Residential
Financing Receivable, Modifications [Line Items]
Weighted average term increase from modificationn	1 year 7 months 6 days	1 year 7 months 6 days	1 year 7 months 6 days
Card
Financing Receivable, Modifications [Line Items]
Weighted average interest rate decrease from modification	16.81%	18.00%	15.22%
Weighted average term increase from modificationn	3 years	3 years	3 years
Decrease in loan principal from modification	¥ 1,118	¥ 862	¥ 809
Krungsri
Financing Receivable, Modifications [Line Items]
Weighted average interest rate decrease from modification	7.97%	4.70%	1.34%
Weighted average term increase from modificationn	3 years 4 months 24 days	3 years 7 months 6 days	2 years 3 months 18 days
Decrease in loan principal from modification	¥ 5,706	¥ 3,524	¥ 1,250
Other
Financing Receivable, Modifications [Line Items]
Weighted average interest rate decrease from modification	2.20%	4.00%	3.40%
Weighted average term increase from modificationn	1 year	1 year	3 years

Amount of increase (decrease) in amortized cost excluding accrued interest, of financing receivable modified for debtor experiencing financial difficulty.

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Percentage of decrease in weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.

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Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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