v3.26.1
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, 2026
Mar. 31, 2025
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gains (losses) for the period included in earnings, Liabilities ¥ 37,213  
Fair value, recurring measurements    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 3,064,178 ¥ 2,472,633
Total gains (losses) for the period included in earnings, Assets 152,113 (19,829)
Total gains (losses) for the period included in other comprehensive income, Assets 43,902 6,260
Purchases, Assets 1,085,543 1,084,871
Issues, Assets (330) (312)
Sales, Assets (79,961) (34,067)
Settlements, Assets (828,268) (502,380)
Transfers into Level 3, Assets 11,608 92,603
Transfers out of Level 3, Assets (90,730) (35,601)
Level 3 assets, Ending balance 3,358,055 3,064,178
Change in unrealized gains (losses) included in earnings for assets still held at period end 208,690 (10,811)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 liabilities, Beginning balance (49,328) 77,885
Total gains (losses) for the period included in earnings, Liabilities   20,351
Total gains (losses) for the period included in other comprehensive income, Liabilities (656) (2,062)
Purchases, Liabilities 0 0
Issues, Liabilities 4,333 0
Sales, Liabilities 0 0
Settlements, Liabilities (7,731) (102,397)
Net transfers into Level 3, Liabilities (50) 0
Transfers out of Level 3, Liabilities 170 (6,527)
Level 3 liabilities, Ending balance (89,163) (49,328)
Change in unrealized gains (losses) included in earnings for liabilities still held at period end ¥ 39,516 27,174
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, 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 ¥ 0 71,399
Total gains (losses) for the period included in earnings, Liabilities   0
Total gains (losses) for the period included in other comprehensive income, Liabilities   0
Purchases, Liabilities   0
Issues, Liabilities   0
Sales, Liabilities   0
Settlements, Liabilities   (71,399)
Transfers into Level 3, Liabilities   0
Transfers out of Level 3, Liabilities   0
Level 3 liabilities, Ending balance   0
Change in unrealized gains (losses) included in earnings for liabilities still held at period end   0
Fair value, recurring measurements | Other    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 liabilities, Beginning balance (49,328) 6,486
Total gains (losses) for the period included in earnings, Liabilities 37,213 20,351
Total gains (losses) for the period included in other comprehensive income, Liabilities (656) (2,062)
Purchases, Liabilities 0 0
Issues, Liabilities 4,333 0
Sales, Liabilities 0 0
Settlements, Liabilities (7,731) (30,998)
Transfers into Level 3, Liabilities (50) 0
Transfers out of Level 3, Liabilities 170 (6,527)
Level 3 liabilities, Ending balance (89,163) (49,328)
Change in unrealized gains (losses) included in earnings for liabilities still held at period end ¥ 39,516 27,174
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Net change during the fiscal year  
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Trading account losses—net  
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, recurring measurements | Trading account, Trading securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance ¥ 2,746,696 2,041,954
Total gains (losses) for the period included in earnings, Assets 161,058 (5,968)
Total gains (losses) for the period included in other comprehensive income, Assets 27,672 (9,121)
Purchases, Assets 1,021,739 1,065,651
Issues, Assets 0 0
Sales, Assets (75,862) (27,371)
Settlements, Assets (818,214) (397,123)
Transfers into Level 3, Assets 15 78,674
Transfers out of Level 3, Assets (72,482) 0
Level 3 assets, Ending balance 2,990,622 2,746,696
Change in unrealized gains (losses) included in earnings for assets still held at period end ¥ 204,939 (22,232)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Net change during the fiscal year  
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 ¥ 0 101
Total gains (losses) for the period included in earnings, Assets   (1)
Total gains (losses) for the period included in other comprehensive income, Assets   0
Purchases, Assets   0
Issues, Assets   0
Sales, Assets   0
Settlements, Assets   (100)
Transfers into Level 3, Assets   0
Transfers out of Level 3, Assets   0
Level 3 assets, Ending balance   0
Change in unrealized gains (losses) included in earnings for assets still held at period end   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 175,464 0
Total gains (losses) for the period included in earnings, Assets 10,876 (812)
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 5,002 99,190
Issues, Assets 0 0
Sales, Assets (4,381) (1,374)
Settlements, Assets 0 0
Transfers into Level 3, Assets 0 78,460
Transfers out of Level 3, Assets (72,482) 0
Level 3 assets, Ending balance 114,479 175,464
Change in unrealized gains (losses) included in earnings for assets still held at period end 10,690 (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 1,816,507 1,352,755
Total gains (losses) for the period included in earnings, Assets 103,284 (10,400)
Total gains (losses) for the period included in other comprehensive income, Assets 27,672 (9,121)
Purchases, Assets 996,075 853,526
Issues, Assets 0 0
Sales, Assets (69,997) (23,091)
Settlements, Assets (764,947) (347,162)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 2,108,594 1,816,507
Change in unrealized gains (losses) included in earnings for assets still held at period end 145,676 (19,985)
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 612,102 536,846
Total gains (losses) for the period included in earnings, Assets 40,797 (1,034)
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 2,000 76,290
Issues, Assets 0 0
Sales, Assets (1,283) 0
Settlements, Assets (39,368) 0
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 614,248 612,102
Change in unrealized gains (losses) included in earnings for assets still held at period end 41,511 (1,034)
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 142,623 152,252
Total gains (losses) for the period included in earnings, Assets 6,101 6,279
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 18,662 36,645
Issues, Assets 0 0
Sales, Assets (201) (2,906)
Settlements, Assets (13,899) (49,861)
Transfers into Level 3, Assets 15 214
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 153,301 142,623
Change in unrealized gains (losses) included in earnings for assets still held at period end 7,062 (440)
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 10,870 58,906
Total gains (losses) for the period included in earnings, Assets (798) (5,605)
Total gains (losses) for the period included in other comprehensive income, Assets 765 1,807
Purchases, Assets 188 669
Issues, Assets (330) (312)
Sales, Assets 0 0
Settlements, Assets (9,617) (23,328)
Transfers into Level 3, Assets 8,654 10,690
Transfers out of Level 3, Assets (3,788) (31,957)
Level 3 assets, Ending balance 5,944 10,870
Change in unrealized gains (losses) included in earnings for assets still held at period end ¥ (2,630) 9,395
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Foreign exchange gains (losses)—net, Trading account losses—net  
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 ¥ (21,934) 39,486
Total gains (losses) for the period included in earnings, Assets (12,552) (18,435)
Total gains (losses) for the period included in other comprehensive income, Assets (644) (706)
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets 831 (6,230)
Transfers into Level 3, Assets 1,479 (3,954)
Transfers out of Level 3, Assets 5,314 (32,095)
Level 3 assets, Ending balance (27,506) (21,934)
Change in unrealized gains (losses) included in earnings for assets still held at period end (8,488) (9,311)
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 25,319 10,198
Total gains (losses) for the period included in earnings, Assets 2,500 (244)
Total gains (losses) for the period included in other comprehensive income, Assets 1,032 1,890
Purchases, Assets 0 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (1,584) (1,505)
Transfers into Level 3, Assets 7,175 14,644
Transfers out of Level 3, Assets (8,836) 336
Level 3 assets, Ending balance 25,606 25,319
Change in unrealized gains (losses) included in earnings for assets still held at period end 3,653 6,113
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 6,603 8,258
Total gains (losses) for the period included in earnings, Assets 9,678 13,373
Total gains (losses) for the period included in other comprehensive income, Assets 377 627
Purchases, Assets 5 0
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (8,734) (15,457)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets (299) (198)
Level 3 assets, Ending balance 7,630 6,603
Change in unrealized gains (losses) included in earnings for assets still held at period end 2,640 12,892
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 (34) (45)
Total gains (losses) for the period included in earnings, Assets 15 30
Total gains (losses) for the period included in other comprehensive income, Assets 0 (4)
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 33 0
Level 3 assets, Ending balance (1) (34)
Change in unrealized gains (losses) included in earnings for assets still held at period end 0 32
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 327 660
Total gains (losses) for the period included in earnings, Assets (129) (212)
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 (115) (121)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 83 327
Change in unrealized gains (losses) included in earnings for assets still held at period end (129) (211)
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 589 349
Total gains (losses) for the period included in earnings, Assets (310) (117)
Total gains (losses) for the period included in other comprehensive income, Assets 0 0
Purchases, Assets 183 669
Issues, Assets (330) (312)
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 132 589
Change in unrealized gains (losses) included in earnings for assets still held at period end (306) (120)
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 197,750 204,805
Total gains (losses) for the period included in earnings, Assets (178) (12,852)
Total gains (losses) for the period included in other comprehensive income, Assets 11,425 12,998
Purchases, Assets 1,722 2,533
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (57) (9,872)
Transfers into Level 3, Assets 1,103 1,631
Transfers out of Level 3, Assets (3,141) (1,493)
Level 3 assets, Ending balance 208,624 197,750
Change in unrealized gains (losses) included in earnings for assets still held at period end ¥ 11,397 199
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
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, 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 ¥ 5,579 5,172
Total gains (losses) for the period included in earnings, Assets (215) 83
Total gains (losses) for the period included in other comprehensive income, Assets 128 (67)
Purchases, Assets 1,684 2,493
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (57) (2,240)
Transfers into Level 3, Assets 1,103 1,631
Transfers out of Level 3, Assets (3,141) (1,493)
Level 3 assets, Ending balance 5,081 5,579
Change in unrealized gains (losses) included in earnings for assets still held at period end 63 34
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 142,284 132,951
Total gains (losses) for the period included in earnings, Assets 0 0
Total gains (losses) for the period included in other comprehensive income, Assets 6,519 9,333
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 148,803 142,284
Change in unrealized gains (losses) included in earnings for assets still held at period end 6,519 9,333
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 49,872 66,667
Total gains (losses) for the period included in earnings, Assets 37 (12,935)
Total gains (losses) for the period included in other comprehensive income, Assets 4,778 3,732
Purchases, Assets 38 40
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets 0 (7,632)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 54,725 49,872
Change in unrealized gains (losses) included in earnings for assets still held at period end 4,815 (9,168)
Fair value, recurring measurements | Equity securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 100,762 87,814
Total gains (losses) for the period included in earnings, Assets (8,610) 4,842
Total gains (losses) for the period included in other comprehensive income, Assets 3,764 447
Purchases, Assets 61,126 14,898
Issues, Assets 0 0
Sales, Assets (4,099) (6,696)
Settlements, Assets 0 0
Transfers into Level 3, Assets 1,836 1,608
Transfers out of Level 3, Assets (11,319) (2,151)
Level 3 assets, Ending balance 143,460 100,762
Change in unrealized gains (losses) included in earnings for assets still held at period end (5,933) 1,944
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 100,762 87,814
Total gains (losses) for the period included in earnings, Assets (8,610) 4,842
Total gains (losses) for the period included in other comprehensive income, Assets 3,764 447
Purchases, Assets 61,126 14,898
Issues, Assets 0 0
Sales, Assets (4,099) (6,696)
Settlements, Assets 0 0
Transfers into Level 3, Assets 1,836 1,608
Transfers out of Level 3, Assets (11,319) (2,151)
Level 3 assets, Ending balance 143,460 100,762
Change in unrealized gains (losses) included in earnings for assets still held at period end (5,933) 1,944
Fair value, recurring measurements | Other    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Level 3 assets, Beginning balance 8,100 79,154
Total gains (losses) for the period included in earnings, Assets 641 (246)
Total gains (losses) for the period included in other comprehensive income, Assets 276 129
Purchases, Assets 768 1,120
Issues, Assets 0 0
Sales, Assets 0 0
Settlements, Assets (380) (72,057)
Transfers into Level 3, Assets 0 0
Transfers out of Level 3, Assets 0 0
Level 3 assets, Ending balance 9,405 8,100
Change in unrealized gains (losses) included in earnings for assets still held at period end ¥ 917 ¥ (117)