v3.25.2
Fair Value (Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Level 3 Inputs) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gains (losses) for the period included in earnings, Liabilities ¥ 20,351  
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Foreign exchange gains (losses)—net, Fees and commissions income (Note 27), Other non-interest income, Investment securities gains (losses)—net (Note 3), Trading account losses—net  
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Foreign exchange gains (losses)—net, Fees and commissions income (Note 27), Other non-interest income, Investment securities gains (losses)—net (Note 3), Trading account losses—net  
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] Net change during the fiscal year  
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] Net change during the fiscal year  
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Trading account losses—net  
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Trading account losses—net  
Fair value, recurring measurements    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance ¥ 2,472,633 ¥ 1,667,416
Total gains (losses) for the period included in earnings, Assets (19,829) 220,341
Total gains (losses) for the period included in other comprehensive income, Assets 6,260 22,944
Purchases, Assets 1,084,871 954,206
Issues, Assets (312) (355)
Sales, Assets (34,067) (18,752)
Settlements, Assets (502,380) (363,362)
Transfers into Level 3, Assets 92,603 51,483
Transfers out of Level 3, Assets (35,601) (61,288)
Level 3 assets, Ending balance 3,064,178 2,472,633
Change in unrealized gains (losses) included in earnings for assets still held at period end (10,811) 223,504
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 liabilities, Beginning balance 77,885 125,325
Total gains (losses) for the period included in earnings, Liabilities   (58,355)
Total gains (losses) for the period included in other comprehensive income, Liabilities (2,062) (8,293)
Purchases, Liabilities 0 0
Issues, Liabilities 0 22,752
Sales, Liabilities 0 0
Settlements, Liabilities (102,397) (113,211)
Transfers into Level 3, Liabilities 0  
Net transfers into Level 3, Liabilities   (705)
Transfers out of Level 3, Liabilities (6,527) (22,924)
Level 3 liabilities, Ending balance (49,328) 77,885
Change in unrealized gains (losses) included in earnings for liabilities still held at period end 27,174 (17,683)
Fair value, recurring measurements | Other    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 liabilities, Beginning balance 6,486 57,121
Total gains (losses) for the period included in earnings, Liabilities 20,351 (58,355)
Total gains (losses) for the period included in other comprehensive income, Liabilities (2,062) (8,293)
Purchases, Liabilities 0 0
Issues, Liabilities 0 17,699
Sales, Liabilities 0 0
Settlements, Liabilities (30,998) (111,353)
Transfers into Level 3, Liabilities 0 (705)
Transfers out of Level 3, Liabilities (6,527) (22,924)
Level 3 liabilities, Ending balance (49,328) 6,486
Change in unrealized gains (losses) included in earnings for liabilities still held at period end 27,174 (17,683)
Fair value, recurring measurements | Obligation to return securities received as collateral    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 liabilities, Beginning balance 71,399 68,204
Total gains (losses) for the period included in earnings, Liabilities 0 0
Total gains (losses) for the period included in other comprehensive income, Liabilities 0 0
Purchases, Liabilities 0 0
Issues, Liabilities 0 5,053
Sales, Liabilities 0 0
Settlements, Liabilities (71,399) (1,858)
Transfers into Level 3, Liabilities 0 0
Transfers out of Level 3, Liabilities 0 0
Level 3 liabilities, Ending balance 0 71,399
Change in unrealized gains (losses) included in earnings for liabilities still held at period end 0 0
Fair value, recurring measurements | Trading account, Trading securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 2,041,954 1,182,319
Total gains (losses) for the period included in earnings, Assets (5,968) 213,607
Total gains (losses) for the period included in other comprehensive income, Assets (9,121) 0
Purchases, Assets 1,065,651 728,692
Issues, Assets 0 0
Sales, Assets (27,371) (16,552)
Settlements, Assets (397,123) (66,257)
Transfers into Level 3, Assets 78,674 145
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 2,746,696 2,041,954
Change in unrealized gains (losses) included in earnings for assets still held at period end (22,232) 206,853
Fair value, recurring measurements | Trading account, Debt securities | Foreign government and official institution bonds    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 101 1,168
Total gains (losses) for the period included in earnings, Assets (1) 123
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 0 7
Issues, Assets 0 0
Sales, Assets 0 (7)
Settlements, Assets (100) (1,190)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 0 101
Change in unrealized gains (losses) included in earnings for assets still held at period end 0 0
Fair value, recurring measurements | Trading account, Debt securities | Corporate bonds    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 0  
Total gains (losses) for the period included in earnings, Assets (812)  
Total gains (losses) for the period included in other comprehensive income, Assets 0  
Purchases, Assets 99,190  
Issues, Assets 0  
Sales, Assets (1,374)  
Settlements, Assets 0  
Transfers into Level 3, Assets 78,460  
Transfers out of Level 3, Assets 0  
Level 3 assets, Ending balance 175,464 0
Change in unrealized gains (losses) included in earnings for assets still held at period end (773)  
Fair value, recurring measurements | Trading account, Debt securities | Asset-backed securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 1,352,755 668,911
Total gains (losses) for the period included in earnings, Assets (10,400) 143,982
Total gains (losses) for the period included in other comprehensive income, Assets (9,121) 0
Purchases, Assets 853,526 552,320
Issues, Assets 0 0
Sales, Assets (23,091) 0
Settlements, Assets (347,162) (12,458)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 1,816,507 1,352,755
Change in unrealized gains (losses) included in earnings for assets still held at period end (19,985) 143,014
Fair value, recurring measurements | Trading account, Debt securities | Other debt securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 536,846 334,124
Total gains (losses) for the period included in earnings, Assets (1,034) 61,722
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 76,290 141,000
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets 0 0
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 612,102 536,846
Change in unrealized gains (losses) included in earnings for assets still held at period end (1,034) 61,722
Fair value, recurring measurements | Trading account, equity securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 152,252 178,116
Total gains (losses) for the period included in earnings, Assets 6,279 7,780
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 36,645 35,365
Issues, Assets 0 0
Sales, Assets (2,906) (16,545)
Settlements, Assets (49,861) (52,609)
Transfers into Level 3, Assets 214 145
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 142,623 152,252
Change in unrealized gains (losses) included in earnings for assets still held at period end (440) 2,117
Fair value, recurring measurements | Trading derivatives—net    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 58,906 81,096
Total gains (losses) for the period included in earnings, Assets (5,605) 1,979
Total gains (losses) for the period included in other comprehensive income, Assets 1,807 1,383
Purchases, Assets 669 423
Issues, Assets (312) (355)
Sales, Assets 0 0
Settlements, Assets (23,328) (16,407)
Transfers into Level 3, Assets 10,690 49,297
Transfers out of Level 3, Assets (31,957) (58,510)
Level 3 assets, Ending balance 10,870 58,906
Change in unrealized gains (losses) included in earnings for assets still held at period end 9,395 1,549
Fair value, recurring measurements | Trading derivatives—net | Interest rate contracts    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 39,486 48,629
Total gains (losses) for the period included in earnings, Assets (18,435) (9,448)
Total gains (losses) for the period included in other comprehensive income, Assets (706) (1,240)
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (6,230) 4,784
Transfers into Level 3, Assets (3,954) 49,324
Transfers out of Level 3, Assets (32,095) (52,563)
Level 3 assets, Ending balance (21,934) 39,486
Change in unrealized gains (losses) included in earnings for assets still held at period end (9,311) (8,541)
Fair value, recurring measurements | Trading derivatives—net | Foreign exchange contracts    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 10,198 11,345
Total gains (losses) for the period included in earnings, Assets (244) 2,429
Total gains (losses) for the period included in other comprehensive income, Assets 1,890 922
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (1,505) (582)
Transfers into Level 3, Assets 14,644 98
Transfers out of Level 3, Assets 336 (4,014)
Level 3 assets, Ending balance 25,319 10,198
Change in unrealized gains (losses) included in earnings for assets still held at period end 6,113 3,309
Fair value, recurring measurements | Trading derivatives—net | Equity contracts    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 8,258 16,928
Total gains (losses) for the period included in earnings, Assets 13,373 10,324
Total gains (losses) for the period included in other comprehensive income, Assets 627 1,694
Purchases, Assets 0 4
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (15,457) (20,415)
Transfers into Level 3, Assets 0 (125)
Transfers out of Level 3, Assets (198) (152)
Level 3 assets, Ending balance 6,603 8,258
Change in unrealized gains (losses) included in earnings for assets still held at period end 12,892 8,070
Fair value, recurring measurements | Trading derivatives—net | Commodity contracts    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance (45) 91
Total gains (losses) for the period included in earnings, Assets 30 (128)
Total gains (losses) for the period included in other comprehensive income, Assets (4) 7
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (15) (15)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance (34) (45)
Change in unrealized gains (losses) included in earnings for assets still held at period end 32 (128)
Fair value, recurring measurements | Trading derivatives—net | Credit derivatives    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 660 3,739
Total gains (losses) for the period included in earnings, Assets (212) (1,119)
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (121) (179)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 (1,781)
Level 3 assets, Ending balance 327 660
Change in unrealized gains (losses) included in earnings for assets still held at period end (211) (1,087)
Fair value, recurring measurements | Trading derivatives—net | Other - net    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 349 364
Total gains (losses) for the period included in earnings, Assets (117) (79)
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 669 419
Issues, Assets (312) (355)
Sales, Assets 0 0
Settlements, Assets 0 0
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 589 349
Change in unrealized gains (losses) included in earnings for assets still held at period end (120) (74)
Fair value, recurring measurements | Available-for-sale debt securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 204,805 253,964
Total gains (losses) for the period included in earnings, Assets (12,852) 1,433
Total gains (losses) for the period included in other comprehensive income, Assets 12,998 21,037
Purchases, Assets 2,533 208,845
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (9,872) (278,573)
Transfers into Level 3, Assets 1,631 26
Transfers out of Level 3, Assets (1,493) (1,927)
Level 3 assets, Ending balance 197,750 204,805
Change in unrealized gains (losses) included in earnings for assets still held at period end 199 12,939
Fair value, recurring measurements | Available-for-sale debt securities | Corporate bonds    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 5,172 2,000
Total gains (losses) for the period included in earnings, Assets 83 (83)
Total gains (losses) for the period included in other comprehensive income, Assets (67) 275
Purchases, Assets 2,493 2,978
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (2,240) (4)
Transfers into Level 3, Assets 1,631 26
Transfers out of Level 3, Assets (1,493) (20)
Level 3 assets, Ending balance 5,579 5,172
Change in unrealized gains (losses) included in earnings for assets still held at period end 34 194
Fair value, recurring measurements | Available-for-sale debt securities | Residential mortgage-backed securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 15 15
Total gains (losses) for the period included in earnings, Assets 0 0
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets 0 0
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 15 15
Change in unrealized gains (losses) included in earnings for assets still held at period end 0 0
Fair value, recurring measurements | Available-for-sale debt securities | Asset-backed securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 132,951 182,938
Total gains (losses) for the period included in earnings, Assets 0 1,597
Total gains (losses) for the period included in other comprehensive income, Assets 9,333 14,325
Purchases, Assets 0 205,611
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets 0 (271,520)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 142,284 132,951
Change in unrealized gains (losses) included in earnings for assets still held at period end 9,333 6,360
Fair value, recurring measurements | Available-for-sale debt securities | Other debt securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 66,667 69,011
Total gains (losses) for the period included in earnings, Assets (12,935) (81)
Total gains (losses) for the period included in other comprehensive income, Assets 3,732 6,437
Purchases, Assets 40 256
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (7,632) (7,049)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 (1,907)
Level 3 assets, Ending balance 49,872 66,667
Change in unrealized gains (losses) included in earnings for assets still held at period end (9,168) 6,385
Fair value, recurring measurements | Equity securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 87,814 74,287
Total gains (losses) for the period included in earnings, Assets 4,842 3,519
Total gains (losses) for the period included in other comprehensive income, Assets 447 383
Purchases, Assets 14,898 10,661
Issues, Assets 0 0
Sales, Assets (6,696) (2,200)
Settlements, Assets 0 0
Transfers into Level 3, Assets 1,608 2,015
Transfers out of Level 3, Assets (2,151) (851)
Level 3 assets, Ending balance 100,762 87,814
Change in unrealized gains (losses) included in earnings for assets still held at period end 1,944 2,360
Fair value, recurring measurements | Equity securities | Nonmarketable equity securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 87,814 74,287
Total gains (losses) for the period included in earnings, Assets 4,842 3,519
Total gains (losses) for the period included in other comprehensive income, Assets 447 383
Purchases, Assets 14,898 10,661
Issues, Assets 0 0
Sales, Assets (6,696) (2,200)
Settlements, Assets 0 0
Transfers into Level 3, Assets 1,608 2,015
Transfers out of Level 3, Assets (2,151) (851)
Level 3 assets, Ending balance 100,762 87,814
Change in unrealized gains (losses) included in earnings for assets still held at period end 1,944 2,360
Fair value, recurring measurements | Other    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 79,154 75,750
Total gains (losses) for the period included in earnings, Assets (246) (197)
Total gains (losses) for the period included in other comprehensive income, Assets 129 141
Purchases, Assets 1,120 5,585
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (72,057) (2,125)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 8,100 79,154
Change in unrealized gains (losses) included in earnings for assets still held at period end ¥ (117) ¥ (197)