Obligations under Guarantees and Other Off-balance Sheet Instruments (Maximum Potential Amount of Future Payments Classified Based upon Internal Credit Ratings) (Detail) - JPY (¥) ¥ in Billions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	¥ 94,556	¥ 86,790
Standby letters of credit and financial guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	6,452	5,992
Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	5,748	4,851
Standby letters of credit, financial and performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	12,200	10,843
Normal \| Standby letters of credit and financial guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	6,336	5,694
Normal \| Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	5,559	4,734
Normal \| Standby letters of credit, financial and performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	¥ 11,895	10,428
Close Watch \| Minimum
Guarantor Obligations [Line Items]
Accruing loans contractually past due, in day	90 days
Close Watch \| Standby letters of credit and financial guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	¥ 91	282
Close Watch \| Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	61	45
Close Watch \| Standby letters of credit, financial and performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	152	327
Likely to become Bankrupt or Legally/Virtually Bankrupt \| Standby letters of credit and financial guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	19	14
Likely to become Bankrupt or Legally/Virtually Bankrupt \| Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	10	23
Likely to become Bankrupt or Legally/Virtually Bankrupt \| Standby letters of credit, financial and performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	29	37
Not rated \| Standby letters of credit and financial guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	6	2
Not rated \| Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	118	49
Not rated \| Standby letters of credit, financial and performance guarantees
Guarantor Obligations [Line Items]
Maximum potential / Contractual or Notional amount, Amount by borrower grade	¥ 124	¥ 51