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, 2022
Mar. 31, 2021
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade ¥ 60,874 ¥ 56,443
Standby letters of credit and financial guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 4,731 4,055
Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 3,828 3,193
Standby letters of credit, financial and performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 8,559 7,248
Normal | Standby letters of credit and financial guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 4,575 3,929
Normal | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 3,706 3,092
Normal | Standby letters of credit, financial and performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade ¥ 8,281 7,021
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 ¥ 121 108
Close Watch | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 73 70
Close Watch | Standby letters of credit, financial and performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 194 178
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 31 15
Likely to become Bankrupt or Legally/Virtually Bankrupt | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 22 3
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 53 18
Not rated | Standby letters of credit and financial guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 4 3
Not rated | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade 27 28
Not rated | Standby letters of credit, financial and performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential / Contractual or Notional amount, Amount by borrower grade ¥ 31 ¥ 31