v3.26.1
Derivative Financial Instruments (Protection Sold Through Credit Default Swaps) (Detail) - Protection sold - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less ¥ 531,028 ¥ 287,633
Maximum potential/Notional amount, Expiring in 1-5 years 1,697,403 1,577,134
Maximum potential/Notional amount, Expiring over 5 years 143,484 213,706
Maximum potential/Notional amount, Total 2,371,915 2,078,473
Credit derivative (asset) liability at fair value (26,935) (27,100)
Single name credit default swaps:    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 236,076 218,344
Maximum potential/Notional amount, Expiring in 1-5 years 820,466 837,625
Maximum potential/Notional amount, Expiring over 5 years 98,761 183,345
Maximum potential/Notional amount, Total 1,155,303 1,239,314
Credit derivative (asset) liability at fair value (12,565) (15,736)
Single name credit default swaps: | Investment grade    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 192,331 185,770
Maximum potential/Notional amount, Expiring in 1-5 years 708,898 710,973
Maximum potential/Notional amount, Expiring over 5 years 93,811 175,920
Maximum potential/Notional amount, Total 995,040 1,072,663
Credit derivative (asset) liability at fair value (15,423) (17,118)
Single name credit default swaps: | Non-investment grade    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 43,745 32,574
Maximum potential/Notional amount, Expiring in 1-5 years 111,568 126,652
Maximum potential/Notional amount, Expiring over 5 years 4,950 7,425
Maximum potential/Notional amount, Total 160,263 166,651
Credit derivative (asset) liability at fair value 2,858 1,382
Index and basket credit default swaps:    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 294,952 69,289
Maximum potential/Notional amount, Expiring in 1-5 years 876,937 739,509
Maximum potential/Notional amount, Expiring over 5 years 44,723 30,361
Maximum potential/Notional amount, Total 1,216,612 839,159
Credit derivative (asset) liability at fair value (14,370) (11,364)
Index and basket credit default swaps: | Investment grade    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 294,952 69,289
Maximum potential/Notional amount, Expiring in 1-5 years 606,595 609,651
Maximum potential/Notional amount, Expiring over 5 years 35,360 22,729
Maximum potential/Notional amount, Total 936,907 701,669
Credit derivative (asset) liability at fair value (8,553) (8,753)
Index and basket credit default swaps: | Not rated    
Credit Derivatives [Line Items]    
Maximum potential/Notional amount, Expiring in 1 year or less 0 0
Maximum potential/Notional amount, Expiring in 1-5 years 270,342 129,858
Maximum potential/Notional amount, Expiring over 5 years 9,363 7,632
Maximum potential/Notional amount, Total 279,705 137,490
Credit derivative (asset) liability at fair value ¥ (5,817) ¥ (2,611)