v3.26.1
Due to Trust Account, Short-term Borrowings and Long-term Debt (Narrative) (Detail)
€ in Millions, ¥ in Millions, $ in Millions
12 Months Ended
Mar. 31, 2026
JPY (¥)
Mar. 31, 2026
USD ($)
Mar. 31, 2026
EUR (€)
Mar. 31, 2025
JPY (¥)
Debt Instrument [Line Items]        
Unused lines of credit for financing ¥ 8,111,352     ¥ 3,439,902
Basel III        
Debt Instrument [Line Items]        
Floor of Common Equity Tier 1 ratio, which leads the Group's discretion over unsecured perpetual subordinated Additional Tier 1 notes 5.125%      
Minimum TLAC ratio, required by end of the period over risk weighted assets 18.00%      
Minimum TLAC ratio, required by end of the period over leverage ratio denominator 7.10%      
Unsecured Perpetual Subordinated Additional Tier 1 Notes | Dollars | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued ¥ 159,880 $ 1,000    
Unsecured Perpetual Subordinated Additional Tier 1 Notes | Yen | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued 350,000      
Bonds for TLAC | Dollars | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued 1,438,920 $ 9,000    
Bonds for TLAC | Yen | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued 40,000      
Bonds for TLAC | Euro | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued 302,627   € 1,650  
Subordinated Tier 2 Notes | Yen | Basel III        
Debt Instrument [Line Items]        
Aggregated principal amount of long term debt issued ¥ 172,000