v3.26.1
Financial Risk Management - Trading Assets and Investment Securities Based on External Rating System (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system ¥ 413,940,083 ¥ 387,253,951
Trading assets [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 6,476,194 5,511,465
Trading assets [member] | AAA [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 79,171 83,484
Trading assets [member] | AA- to AA+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 5,237,512 4,473,308
Trading assets [member] | A- to A+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 531,789 369,924
Trading assets [member] | Lower than A- [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 486,384 451,490
Trading assets [member] | Unrated [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 41,955 67,712
Trading assets [member] | External credit grades [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 6,376,811 5,445,918
Financial assets at fair value through profit or loss [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 2,620,759 2,820,665
Financial assets at fair value through profit or loss [member] | AA- to AA+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 25,440 26,006
Financial assets at fair value through profit or loss [member] | A- to A+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 4,515 11,871
Financial assets at fair value through profit or loss [member] | Lower than A- [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 63,751 142,241
Financial assets at fair value through profit or loss [member] | Unrated [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 24,650 12,657
Financial assets at fair value through profit or loss [member] | External credit grades [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 118,356 192,775
Debt instruments at amortized cost [member] | AAA [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 69,872  
Debt instruments at amortized cost [member] | AA- to AA+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 4,599,948 288,291
Debt instruments at amortized cost [member] | Lower than A- [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 83,011 66,895
Debt instruments at amortized cost [member] | Unrated [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 10,885 11,811
Debt instruments at amortized cost [member] | External credit grades [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 4,763,716 366,997
Debt instruments at fair value through other comprehensive income [member] | AAA [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 3,312,698 2,759,838
Debt instruments at fair value through other comprehensive income [member] | AA- to AA+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 17,582,729 23,489,895
Debt instruments at fair value through other comprehensive income [member] | A- to A+ [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 1,428,237 1,075,246
Debt instruments at fair value through other comprehensive income [member] | Lower than A- [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 1,316,287 1,115,603
Debt instruments at fair value through other comprehensive income [member] | Unrated [Member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system 231,510 205,583
Debt instruments at fair value through other comprehensive income [member] | External credit grades [member]    
Disclosure of external credit grades [line items]    
Trading assets and investment securities based on the external rating system ¥ 23,871,461 ¥ 28,646,165