v3.26.1
Fair value measurements - Schedule of unrealized gains and losses recognized for Level 3 financial instruments (Detail) - Recurring [Member] - Level 3 [Member] - JPY (¥)
¥ in Billions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] ¥ 56 ¥ (40)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Revenues Revenues
Unrealized gains/(losses), Liabilities [1] ¥ 6 ¥ 18
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Revenues Revenues
Trading assets and private equity and debt investments [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] ¥ (4) ¥ (17)
Trading assets and private equity and debt investments [Member] | Equities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] (1) 0
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 1 (1)
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 1 0
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 5 (6)
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 0 7
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] (2) 2
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] (3) 5
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] (5) (24)
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 0 0
Equity contracts [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] 19 (3)
Interest rate contracts [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] (2) (23)
Credit contracts [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] (16) (26)
Foreign exchange contracts [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] (11) (7)
Other contracts [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] (2) 2
Derivatives, net [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1],[2] (12) (57)
Subtotal [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] (16) (74)
Loans and receivables [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 22 14
Collateralized agreements [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 0 0
Non-Trading debt Securities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 1 0
Other [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Assets [1] 49 20
Trading liabilities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1] 0 1
Trading liabilities [Member] | Equities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1] 0 0
Trading liabilities [Member] | Bank and corporate debt securities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1] 0 0
Trading liabilities [Member] | Collateralized debt obligations ("CDOs") and other [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1] 0 1
Short-term borrowings [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1],[3] 1 (7)
Payables and deposits [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1],[3] 1 1
Long-term borrowings [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1],[3] 5 24
Other liabilities [Member]    
Fair value, assets and liabilities measured on recurring basis, unobservable input reconciliation [Line items]    
Unrealized gains/(losses), Liabilities [1] ¥ (1) ¥ (1)
[1] Includes gains and losses reported within Net gain on trading, Gain on private equity and debt investments, and also within Gain(loss) on investments in equity securities, Revenue—Other and Non-interest expenses—Other, Interest and dividends and Interest expense in the consolidated statements of income.
[2] Derivatives which contain multiple types of risk are classified based on the primary risk type of the instrument.
[3] Includes unrealized gains and losses of ¥10 billion and ¥(1) billion for the years ended March 31, 2025 and 2026 recognized in Other comprehensive income (loss) for recurring Level 3 fair value measurements held at the end of the reporting period.