v3.26.1
Commitments and Contingencies (Summary of Maximum Potential Amount of Future Payments under Guarantees) (Detail) - JPY (¥)
¥ in Billions
Mar. 31, 2026
Mar. 31, 2025
Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount ¥ 4,777 ¥ 4,100
Guarantees on loans    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 244 220
Guarantees on securities    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 131 92
Other guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 3,793 3,309
Guarantees for repayment of trust principal    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 7 11
Liabilities of trust accounts    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 404 330
Derivative financial instruments    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 75,897 80,505
One year or less | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 2,644 2,233
One year or less | Guarantees on loans    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 199 126
One year or less | Guarantees on securities    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 30 0
One year or less | Other guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 3,043 2,709
One year or less | Guarantees for repayment of trust principal    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 0 0
One year or less | Liabilities of trust accounts    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 129 98
One year or less | Derivative financial instruments    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 44,514 38,199
After one year through five years | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 1,852 1,651
After one year through five years | Guarantees on loans    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 32 79
After one year through five years | Guarantees on securities    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 101 92
After one year through five years | Other guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 642 494
After one year through five years | Guarantees for repayment of trust principal    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 0 2
After one year through five years | Liabilities of trust accounts    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 51 61
After one year through five years | Derivative financial instruments    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 25,480 35,858
After five years | Performance guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 281 217
After five years | Guarantees on loans    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 12 15
After five years | Guarantees on securities    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 0 0
After five years | Other guarantees    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 109 106
After five years | Guarantees for repayment of trust principal    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 7 8
After five years | Liabilities of trust accounts    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount 224 171
After five years | Derivative financial instruments    
Guarantor Obligations [Line Items]    
Maximum potential/Contractual or Notional amount ¥ 5,903 ¥ 6,448