v3.26.1
Derivative Financial Instruments and Hedge Accounting - Schedule of Items Designated as Hedging Instruments (Detail) - Interest rate risk [Member] - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Interest rate swaps [Member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts ¥ 10,792,370 ¥ 9,345,733
Carrying amounts, Assets 102,943 121,920
Carrying amounts, Liabilities 381,753 420,524
Change in value used for calculating hedge ineffectiveness (144,319) (35,197)
Interest rate option [Member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 222,261 207,847
Carrying amounts, Assets
Carrying amounts, Liabilities 39,169 34,926
Change in value used for calculating hedge ineffectiveness (6,717) (3,758)
Debt instruments [Member]    
Disclosure of detailed information about financial instruments [line items]    
Change in value used for calculating hedge ineffectiveness 121,570 (6,919)
Carrying amounts 9,530,328 8,195,943
Borrowings [Member]    
Disclosure of detailed information about financial instruments [line items]    
Change in value used for calculating hedge ineffectiveness 4,158 1,492
Carrying amounts 122,354 120,304
Investment securities [Member]    
Disclosure of detailed information about financial instruments [line items]    
Change in value used for calculating hedge ineffectiveness 29,165 43,785
Carrying amounts ¥ 888,319 ¥ 810,009