v3.26.1
Fair Value of Financial Assets and Liabilities - Total and Changes in Unrealized Gains or Losses Included in Profit or Loss for Level 3 Financial Assets and Liabilities (Detail) - At fair value [member] - Level 3 [member] - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Total gains (losses) included in profit or loss ¥ 32,760 ¥ (900)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held 37,713 1,134
Net interest income [Member]    
Disclosure of detailed information about financial instruments [line items]    
Total gains (losses) included in profit or loss 1,583 1,865
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held 606 705
Net trading income    
Disclosure of detailed information about financial instruments [line items]    
Total gains (losses) included in profit or loss 12,796 7,043
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held 14,622 8,850
Net income (loss) from financial assets and liabilities at fair value through profit or loss [Member]    
Disclosure of detailed information about financial instruments [line items]    
Total gains (losses) included in profit or loss 18,381 (9,808)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held ¥ 22,485 ¥ (8,421)