v3.26.1
Fair Value of Financial Assets and Liabilities - Reconciliations for Financial Assets and Liabilities Carried at Fair Value (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Transfers into Level 3 ¥ 72,155 ¥ 39,417
Transfers out of Level 3 (2,297) (6,634)
At fair value [member] | Level 3 [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 1,403,049 1,225,315
Total gains (losses), Included in profit or loss 32,760 (900)
Total gains (losses), Included in other comprehensive income 49,055 30,836
Purchases 298,161 319,928
Sales (188,383) (67,965)
Issuances (14,100) (26,075)
Settlement (121,841) (110,873)
Transfers into Level 3 72,155 39,417
Transfers out of Level 3 (2,297) (6,634)
Ending balance 1,528,559 1,403,049
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance 37,713 1,134
At fair value [member] | Level 3 [member] | Financial liabilities at fair value through profit or loss, category [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance (129,678) (125,042)
Total gains (losses), Included in profit or loss 4,123 1,298
Total gains (losses), Included in other comprehensive income 140 1,248
Issuances (14,100) (26,075)
Settlement 17,838 18,893
Ending balance (121,677) (129,678)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance 4,145 3,129
At fair value [member] | Level 3 [member] | Trading assets [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 41,380  
Total gains (losses), Included in profit or loss 867 500
Purchases   1,558
Sales (42,247)  
Transfers into Level 3   39,322
Ending balance   41,380
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance   500
At fair value [member] | Level 3 [member] | Trading assets [member] | Debt instruments [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 41,380  
Total gains (losses), Included in profit or loss 867 500
Purchases   1,558
Sales (42,247)  
Transfers into Level 3   39,322
Ending balance   41,380
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance   500
At fair value [member] | Level 3 [member] | Derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance (2,484) 117
Total gains (losses), Included in profit or loss (4,996) (2,091)
Purchases 5,295 8,301
Sales (5,571) (8,811)
Ending balance (7,756) (2,484)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance (2,552) 466
At fair value [member] | Level 3 [member] | Derivatives [member] | Interest rate derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance (4,173) (2,656)
Total gains (losses), Included in profit or loss (6,413) (3,067)
Purchases 4,092 1,802
Sales (1,204) (252)
Ending balance (7,698) (4,173)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance (3,555) (1,510)
At fair value [member] | Level 3 [member] | Derivatives [member] | Currency derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance (1,891) (923)
Total gains (losses), Included in profit or loss 172 (968)
Ending balance (1,719) (1,891)
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance (58) (887)
At fair value [member] | Level 3 [member] | Derivatives [member] | Equity derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 3,379 3,382
Total gains (losses), Included in profit or loss 1,368 2,057
Purchases 1,203 6,499
Sales (4,367) (8,559)
Ending balance 1,583 3,379
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance 1,181 2,947
At fair value [member] | Level 3 [member] | Derivatives [member] | Credit derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 201 314
Total gains (losses), Included in profit or loss (123) (113)
Ending balance 78 201
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance (120) (84)
At fair value [member] | Level 3 [member] | Financial assets at fair value through profit or loss [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 929,266 819,144
Total gains (losses), Included in profit or loss 14,258 (11,106)
Total gains (losses), Included in other comprehensive income 233 (42)
Purchases 278,694 305,346
Sales (134,176) (51,839)
Settlement (138,986) (129,348)
Transfers out of Level 3 (2,136) (2,889)
Ending balance 947,153 929,266
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance 18,340 (11,550)
At fair value [member] | Level 3 [member] | Financial assets at fair value through profit or loss [member] | Debt instruments [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 849,122 739,914
Total gains (losses), Included in profit or loss 20,518 (7,237)
Total gains (losses), Included in other comprehensive income 233 (42)
Purchases 261,181 291,778
Sales (132,211) (48,335)
Settlement (133,122) (124,379)
Transfers out of Level 3 (886) (2,577)
Ending balance 864,835 849,122
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance 26,022 (5,321)
At fair value [member] | Level 3 [member] | Financial assets at fair value through profit or loss [member] | Equity instruments [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 80,144 79,230
Total gains (losses), Included in profit or loss (6,260) (3,869)
Purchases 17,513 13,568
Sales (1,965) (3,504)
Settlement (5,864) (4,969)
Transfers out of Level 3 (1,250) (312)
Ending balance 82,318 80,144
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance (7,682) (6,229)
At fair value [member] | Level 3 [member] | Financial assets at fair value through other comprehensive income, category [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 550,448 525,869
Total gains (losses), Included in other comprehensive income 48,682 29,630
Purchases 14,172 4,723
Sales (6,389) (7,315)
Settlement (693) (418)
Transfers into Level 3 72,155 95
Transfers out of Level 3   (2,136)
Ending balance 678,375 550,448
At fair value [member] | Level 3 [member] | Financial assets at fair value through other comprehensive income, category [member] | Equity instruments [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 550,448 525,869
Total gains (losses), Included in other comprehensive income 48,682 29,630
Purchases 14,172 4,723
Sales (6,389) (7,315)
Settlement (693) (418)
Transfers into Level 3 72,155 95
Transfers out of Level 3   (2,136)
Ending balance 678,375 550,448
At fair value [member] | Level 3 [member] | Others-liabilities [member]    
Disclosure of detailed information about financial instruments [line items]    
Beginning balance 14,117 5,227
Total gains (losses), Included in profit or loss 18,508 10,499
Transfers out of Level 3 (161) (1,609)
Ending balance 32,464 14,117
Changes in unrealized gains (losses) included in profit or loss related to assets and liabilities held at ending balance ¥ 17,780 ¥ 8,589