v3.26.1
Fair Value (Items Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - JPY (¥)
¥ in Billions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Long-term debt    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance ¥ 489 ¥ 427
Gains (losses) in Earnings [1] (2) 22
Gains (losses) in OCI [2] (6) 6
Transfers into Level 3 41 7
Transfers out of level 3 (5)  
Purchases 0  
Sales 0  
Issuances 281 250
Settlements (244) (168)
Ending Balance 569 489
Change in unrealized gain (losses) still held [3] 7 30
Other liabilities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 37  
Gains (losses) in Earnings 0  
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 3 37
Settlements 0  
Ending Balance 40 37
Change in unrealized gain (losses) still held 0  
Trading securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Transfers into Level 3 20  
Trading securities | Corporate bonds and other debt securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 174 189
Gains (losses) in Earnings [4] 19 3
Gains (losses) in OCI 0  
Transfers into Level 3 20  
Transfers out of level 3 0  
Purchases 225 47
Sales (160) (61)
Issuances 0  
Settlements (102) (5)
Ending Balance 177 174
Change in unrealized gain (losses) still held [3] 34 2
Trading securities | Equity securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 21 21
Gains (losses) in Earnings [4] 0 1
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 0  
Settlements 0 (1)
Ending Balance 21 21
Change in unrealized gain (losses) still held [3] 0 1
Derivative financial instruments assets    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance [5] 1  
Transfers into Level 3 6  
Transfers out of level 3 (1)  
Ending Balance [5]   1
Derivative financial instruments assets | Interest rate contracts    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance [5] (2) 13
Gains (losses) in Earnings (2) (13) [4],[5]
Gains (losses) in OCI 0  
Transfers into Level 3 6  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 0  
Settlements (6) (2) [5]
Ending Balance (4) (2) [5]
Change in unrealized gain (losses) still held [3],[5] (6) (13)
Derivative financial instruments assets | Foreign exchange contracts    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance [5] 6 (9)
Gains (losses) in Earnings (7) 11 [4],[5]
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 0  
Settlements 4 4 [5]
Ending Balance 3 6 [5]
Change in unrealized gain (losses) still held [3],[5] (1) 12
Derivative financial instruments assets | Equity-related contracts    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance [5] (73) (70)
Gains (losses) in Earnings (113) (11) [4],[5]
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 0  
Settlements 29 8 [5]
Ending Balance (156) (73) [5]
Change in unrealized gain (losses) still held [3],[5] (44) (10)
Derivative financial instruments assets | Credit-related contracts    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance [5] (2) (5)
Gains (losses) in Earnings (1)  
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 0  
Sales 0  
Issuances 0  
Settlements 4 3 [5]
Ending Balance 1 (2) [5]
Change in unrealized gain (losses) still held [3],[5] 5 (1)
Derivative financial instruments assets | Other contracts    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 1  
Gains (losses) in Earnings (4) 2 [4],[5]
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 (1)  
Purchases 0  
Sales 0  
Issuances 0  
Settlements 2  
Ending Balance (1) 1
Change in unrealized gain (losses) still held [3],[5] (1) 2
Available-for-sale securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Transfers out of level 3 (3) (11)
Available-for-sale securities | Residential mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 6 8
Gains (losses) in Earnings [6] (1)  
Gains (losses) in OCI [2] 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 11  
Sales (3)  
Issuances 0  
Settlements (1) (1)
Ending Balance 12 6
Change in unrealized gain (losses) still held [3] 0  
Available-for-sale securities | Commercial mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 3 4
Gains (losses) in Earnings [6] 0  
Gains (losses) in OCI [2] 0  
Transfers into Level 3 0  
Transfers out of level 3 (3) (1)
Purchases 0  
Sales 0  
Issuances 0  
Settlements 0  
Ending Balance 0 3
Change in unrealized gain (losses) still held [3] 0  
Available-for-sale securities | Japanese corporate bonds and other debt securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 186 167
Gains (losses) in Earnings [6] 0  
Gains (losses) in OCI [2] (6) (10)
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 61 35
Sales 0  
Issuances 0  
Settlements (13) (7)
Ending Balance 228 186
Change in unrealized gain (losses) still held [3] (6) (9)
Available-for-sale securities | Foreign corporate bonds and other debt securities    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 13 23
Gains (losses) in Earnings [6] 0  
Gains (losses) in OCI [2] 0  
Transfers into Level 3 0  
Transfers out of level 3 0 (10)
Purchases 0  
Sales 0  
Issuances 0  
Settlements (13)  
Ending Balance 0 13
Change in unrealized gain (losses) still held [3] 0  
Available-for-sale securities | Other investments    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 86 80
Gains (losses) in Earnings [6] (1)  
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0 (2)
Purchases 60 55
Sales 0 (1)
Issuances 0  
Settlements (55) (46)
Ending Balance 89 86
Change in unrealized gain (losses) still held [3] 1 (2)
Other assets    
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning Balance 37  
Gains (losses) in Earnings 0  
Gains (losses) in OCI 0  
Transfers into Level 3 0  
Transfers out of level 3 0  
Purchases 3 37
Sales 0  
Issuances 0  
Settlements 0  
Ending Balance 40 ¥ 37
Change in unrealized gain (losses) still held [3] ¥ 0  
[1] Gains (losses) in Earnings are reported in Other noninterest income (expenses).
[2] Gains (losses) in OCI are reported in Other comprehensive income (loss).
[3] Amounts represent total gains or losses recognized in earnings and other comprehensive income (loss) during the period. These gains or losses were attributable to the change in fair value relating to assets and liabilities classified as Level 3 that were still held at March 31, 2025 and 2026. The amounts of unrealized gains (losses) in other comprehensive income (loss) are related to Available-for-sale securities and Long-term debt, which were ¥(10) billion and ¥6 billion, respectively, at March 31, 2025, and ¥(6) billion and ¥(6) billion, respectively, at March 31, 2026.
[4] Gains (losses) in Earnings are reported in Trading account gains (losses)—net, Foreign exchange gains (losses)—net or Other noninterest income (expenses).
[5] Total Level 3 derivative exposures have been netted on the table for presentation purposes only.
[6] Gains (losses) in Earnings are reported in Investment gains (losses)—net.