v3.26.1
Pledged Assets and Collateral (Narrative) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Financial Instruments Owned and Pledged as Collateral [Line Items]      
Investment securities pledged for acting as a collection agent of public funds ¥ 29,280,388    
Reserve funds included in Cash and due from banks and Interest-earning deposits in other banks 3,128,833 ¥ 2,962,933  
Total assets at end of fiscal year 425,581,652 405,940,211 ¥ 397,820,570
Fair value of securities accepted as collateral that is permitted to be sold or repledged 41,810,000 41,438,000  
Fair value of securities accepted as collateral that was sold or repledged 28,675,000 29,714,000  
Cash collateral pledged for derivative transactions included in Other assets 4,261,209 2,566,588  
Cash collateral received for derivative transactions included in Other liabilities 1,417,988 ¥ 1,415,939  
Asset pledged as collateral without right      
Financial Instruments Owned and Pledged as Collateral [Line Items]      
Total assets at end of fiscal year ¥ 28,981,000