v3.26.1
Investment Securities (Narrative) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Investment Securities [Line Items]      
Gross realized gains on sales of Available-for-sale debt securities ¥ 57,226 ¥ 49,923 ¥ 124,557
Gross realized losses on sales of available-for-sale debt securities 366,176 200,679 274,042
Investment securities gains (losses)—net (666,069) 832,533 (1,382,458)
Japanese national government and Japanese government agency bonds      
Investment Securities [Line Items]      
Investment securities credit loss 0    
Investment securities impairment loss 0    
Japanese prefectural and municipal bonds      
Investment Securities [Line Items]      
Investment securities credit loss 0    
Investment securities impairment loss 0    
Foreign government and official institution bonds      
Investment Securities [Line Items]      
Investment securities credit loss 0    
Investment securities impairment loss 0    
Residential mortgage-backed securities      
Investment Securities [Line Items]      
Investment securities credit loss 0    
Investment securities impairment loss 0    
Asset-backed securities      
Investment Securities [Line Items]      
Investment securities credit loss 0    
Investment securities impairment loss 0    
Other debt securities      
Investment Securities [Line Items]      
Investment securities gains (losses)—net ¥ 0 ¥ 12,988 ¥ 0