v3.26.1
Fair value measurements - Schedule of movements in Level 3 financial instruments (Detail) - Recurring [Member] - Level 3 [Member] - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Assets [Abstract]    
Beginning balance, Assets ¥ 1,330,000 ¥ 1,041,000
Total gains (losses) recognized in net income, Assets [1] ¥ 74,000 ¥ (25,000)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Net revenues Net revenues
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 1,046,000 1,121,000
Sales/ redemptions, Assets [2] (1,094,000) (1,019,000)
Settlements, Assets (16,000) 41,000
Foreign exchange movements, Assets 90,000 (30,000)
Transfers into Level 3, Assets [3],[4] 293,000 319,000
Transfers out of Level 3, Assets [4],[5] (433,000) (118,000)
Ending balance, Assets 1,290,000 1,330,000
Liabilities [Abstract]    
Beginning balance, Liabilities 593,000 557,000
Total gains (losses) recognized in net income, Liabilities [1] ¥ (19,000) ¥ 0
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Revenues Revenues
Total gains (losses) recognized in other comprehensive income, Liabilities ¥ (3,000) ¥ 9,000
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), Net of Tax
Purchases/ issues, Liabilities [2] ¥ 391,000 ¥ 341,000
Sales/ redemptions, Liabilities [2] (363,000) (243,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 8,000 (1,000)
Transfers into Level 3, Liabilities [3],[4] 24,000 13,000
Transfers out of Level 3, Liabilities [4],[5] (100,000) (65,000)
Ending balance, Liabilities 575,000 593,000
Trading assets and private equity and debt investments [Member]    
Assets [Abstract]    
Beginning balance, Assets 621,000 470,000
Total gains (losses) recognized in net income, Assets [1] 2,000 (12,000)
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 719,000 872,000
Sales/ redemptions, Assets [2] (702,000) (767,000)
Settlements, Assets
Foreign exchange movements, Assets 27,000 (7,000)
Transfers into Level 3, Assets [3],[4] 82,000 100,000
Transfers out of Level 3, Assets [4],[5] (346,000) (35,000)
Ending balance, Assets 403,000 621,000
Trading assets and private equity and debt investments [Member] | Equities [Member]    
Assets [Abstract]    
Beginning balance, Assets 21,000 8,000
Total gains (losses) recognized in net income, Assets [1] 0 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 16,000 17,000
Sales/ redemptions, Assets [2] (36,000) (13,000)
Settlements, Assets
Foreign exchange movements, Assets 2,000 1,000
Transfers into Level 3, Assets [3],[4] 14,000 15,000
Transfers out of Level 3, Assets [4],[5] (3,000) (7,000)
Ending balance, Assets 14,000 21,000
Trading assets and private equity and debt investments [Member] | Private equity and debt investments [Member]    
Assets [Abstract]    
Beginning balance, Assets 103,000 80,000
Total gains (losses) recognized in net income, Assets [1] 5,000 3,000
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 101,000 37,000
Sales/ redemptions, Assets [2] (44,000) (9,000)
Settlements, Assets
Foreign exchange movements, Assets 1,000 0
Transfers into Level 3, Assets [3],[4] 1,000
Transfers out of Level 3, Assets [4],[5] (21,000) (8,000)
Ending balance, Assets 146,000 103,000
Trading assets and private equity and debt investments [Member] | Japanese agency and municipal securities [Member]    
Assets [Abstract]    
Beginning balance, Assets 0 0
Total gains (losses) recognized in net income, Assets [1] 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 2,000
Sales/ redemptions, Assets [2] (2,000) 0
Settlements, Assets
Foreign exchange movements, Assets
Transfers into Level 3, Assets [3],[4]
Transfers out of Level 3, Assets [4],[5]
Ending balance, Assets   0
Trading assets and private equity and debt investments [Member] | Foreign government, agency and municipal securities [Member]    
Assets [Abstract]    
Beginning balance, Assets 6,000 3,000
Total gains (losses) recognized in net income, Assets [1] 1,000 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 5,000 5,000
Sales/ redemptions, Assets [2] (6,000) (5,000)
Settlements, Assets
Foreign exchange movements, Assets 0 0
Transfers into Level 3, Assets [3],[4] 4,000 7,000
Transfers out of Level 3, Assets [4],[5] (6,000) (4,000)
Ending balance, Assets 4,000 6,000
Trading assets and private equity and debt investments [Member] | Bank and corporate debt securities and loans for trading purposes [Member]    
Assets [Abstract]    
Beginning balance, Assets 181,000 173,000
Total gains (losses) recognized in net income, Assets [1] 8,000 (5,000)
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 103,000 205,000
Sales/ redemptions, Assets [2] (182,000) (240,000)
Settlements, Assets
Foreign exchange movements, Assets 13,000 (5,000)
Transfers into Level 3, Assets [3],[4] 39,000 69,000
Transfers out of Level 3, Assets [4],[5] (58,000) (16,000)
Ending balance, Assets 104,000 181,000
Trading assets and private equity and debt investments [Member] | Commercial mortgage-backed securities ("CMBS") [Member]    
Assets [Abstract]    
Beginning balance, Assets 10,000 0
Total gains (losses) recognized in net income, Assets [1] 0 2,000
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 0 7,000
Sales/ redemptions, Assets [2] (10,000) (6,000)
Settlements, Assets
Foreign exchange movements, Assets
Transfers into Level 3, Assets [3],[4] 7,000
Transfers out of Level 3, Assets [4],[5] 0
Ending balance, Assets 0 10,000
Trading assets and private equity and debt investments [Member] | Residential mortgage-backed securities ("RMBS") [Member]    
Assets [Abstract]    
Beginning balance, Assets 48,000 35,000
Total gains (losses) recognized in net income, Assets [1] (3,000) 2,000
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 3,000 56,000
Sales/ redemptions, Assets [2] (20,000) (46,000)
Settlements, Assets
Foreign exchange movements, Assets 2,000 (1,000)
Transfers into Level 3, Assets [3],[4] 1,000 2,000
Transfers out of Level 3, Assets [4],[5] (21,000) 0
Ending balance, Assets 10,000 48,000
Trading assets and private equity and debt investments [Member] | Real estate-backed securities [Member]    
Assets [Abstract]    
Beginning balance, Assets 207,000 122,000
Total gains (losses) recognized in net income, Assets [1] 0 11,000
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 362,000 370,000
Sales/ redemptions, Assets [2] (287,000) (294,000)
Settlements, Assets
Foreign exchange movements, Assets 8,000 (2,000)
Transfers into Level 3, Assets [3],[4] 18,000
Transfers out of Level 3, Assets [4],[5] (226,000)
Ending balance, Assets 82,000 207,000
Trading assets and private equity and debt investments [Member] | Collateralized debt obligations ("CDOs") and other [Member]    
Assets [Abstract]    
Beginning balance, Assets 42,000 46,000
Total gains (losses) recognized in net income, Assets [1] (9,000) (25,000)
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 39,000 107,000
Sales/ redemptions, Assets [2] (36,000) (86,000)
Settlements, Assets
Foreign exchange movements, Assets 1,000 0
Transfers into Level 3, Assets [3],[4] 0
Transfers out of Level 3, Assets [4],[5] (3,000) 0
Ending balance, Assets 34,000 42,000
Trading assets and private equity and debt investments [Member] | Investment trust funds and other [Member]    
Assets [Abstract]    
Beginning balance, Assets 3,000 3,000
Total gains (losses) recognized in net income, Assets [1] 0 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 88,000 68,000
Sales/ redemptions, Assets [2] (79,000) (68,000)
Settlements, Assets
Foreign exchange movements, Assets 0 0
Transfers into Level 3, Assets [3],[4] 5,000 0
Transfers out of Level 3, Assets [4],[5] (8,000)
Ending balance, Assets 9,000 3,000
Equity contracts [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] 1,000 5,000
Total gains (losses) recognized in net income, Assets [1],[6] 2,000 0
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] 32,000 (5,000)
Foreign exchange movements, Assets [6] (1,000) 0
Transfers into Level 3, Assets [3],[4],[6] (15,000) 0
Transfers out of Level 3, Assets [4],[5],[6] 8,000 1,000
Ending balance, Assets [6] 27,000 1,000
Interest rate contracts [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] 6,000 32,000
Total gains (losses) recognized in net income, Assets [1],[6] 16,000 (20,000)
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] (29,000) 12,000
Foreign exchange movements, Assets [6] 2,000 (4,000)
Transfers into Level 3, Assets [3],[4],[6] 8,000 (19,000)
Transfers out of Level 3, Assets [4],[5],[6] (19,000) 5,000
Ending balance, Assets [6] (16,000) 6,000
Credit contracts [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] (36,000) (46,000)
Total gains (losses) recognized in net income, Assets [1],[6] 2,000 (30,000)
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] (25,000) 37,000
Foreign exchange movements, Assets [6] (2,000) 1,000
Transfers into Level 3, Assets [3],[4],[6] 12,000 (1,000)
Transfers out of Level 3, Assets [4],[5],[6] (7,000) 3,000
Ending balance, Assets [6] (56,000) (36,000)
Foreign exchange contracts [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] (13,000) 3,000
Total gains (losses) recognized in net income, Assets [1],[6] (12,000) (9,000)
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] 4,000 (5,000)
Foreign exchange movements, Assets [6] 1,000 0
Transfers into Level 3, Assets [3],[4],[6] (1,000) 0
Transfers out of Level 3, Assets [4],[5],[6] (1,000) (2,000)
Ending balance, Assets [6] (22,000) (13,000)
Other contracts [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] (4,000)
Total gains (losses) recognized in net income, Assets [1],[6] (2,000) 2,000
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] 2,000 1,000
Foreign exchange movements, Assets [6] 0 (2,000)
Transfers into Level 3, Assets [3],[4],[6] 2,000 (5,000)
Transfers out of Level 3, Assets [4],[5],[6]
Ending balance, Assets [6] (2,000) (4,000)
Derivatives, net [Member]    
Assets [Abstract]    
Beginning balance, Assets [6] (46,000) (6,000)
Total gains (losses) recognized in net income, Assets [1],[6] 6,000 (57,000)
Total gains (losses) recognized in other comprehensive income, Assets [6]
Purchases/ issues, Assets [2],[6]
Sales/ redemptions, Assets [2],[6]
Settlements, Assets [6] (16,000) 40,000
Foreign exchange movements, Assets [6] 0 (5,000)
Transfers into Level 3, Assets [3],[4],[6] 6,000 (25,000)
Transfers out of Level 3, Assets [4],[5],[6] (19,000) 7,000
Ending balance, Assets [6] (69,000) (46,000)
Subtotal [Member]    
Assets [Abstract]    
Beginning balance, Assets 575,000 464,000
Total gains (losses) recognized in net income, Assets [1] 8,000 (69,000)
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 719,000 872,000
Sales/ redemptions, Assets [2] (702,000) (767,000)
Settlements, Assets (16,000) 40,000
Foreign exchange movements, Assets 27,000 (12,000)
Transfers into Level 3, Assets [3],[4] 88,000 75,000
Transfers out of Level 3, Assets [4],[5] (365,000) (28,000)
Ending balance, Assets 334,000 575,000
Loans and receivables [Member]    
Assets [Abstract]    
Beginning balance, Assets 448,000 291,000
Total gains (losses) recognized in net income, Assets [1] 32,000 24,000
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 237,000 199,000
Sales/ redemptions, Assets [2] (285,000) (234,000)
Settlements, Assets
Foreign exchange movements, Assets 40,000 (14,000)
Transfers into Level 3, Assets [3],[4] 178,000 244,000
Transfers out of Level 3, Assets [4],[5] (66,000) (62,000)
Ending balance, Assets 584,000 448,000
Collateralized agreements [Member]    
Assets [Abstract]    
Beginning balance, Assets 15,000 12,000
Total gains (losses) recognized in net income, Assets [1] 0 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 2,000
Sales/ redemptions, Assets [2]
Settlements, Assets 1,000
Foreign exchange movements, Assets 1,000 0
Transfers into Level 3, Assets [3],[4]
Transfers out of Level 3, Assets [4],[5]
Ending balance, Assets 16,000 15,000
Non-trading debt securities [Member]    
Assets [Abstract]    
Beginning balance, Assets 17,000 21,000
Total gains (losses) recognized in net income, Assets [1] 2,000 0
Total gains (losses) recognized in other comprehensive income, Assets
Purchases/ issues, Assets [2] 10,000 3,000
Sales/ redemptions, Assets [2] (8,000) (7,000)
Settlements, Assets
Foreign exchange movements, Assets 1,000 0
Transfers into Level 3, Assets [3],[4] 26,000
Transfers out of Level 3, Assets [4],[5]
Ending balance, Assets 48,000 17,000
Other [Member]    
Assets [Abstract]    
Beginning balance, Assets [7] 275,000 [8] 253,000
Total gains (losses) recognized in net income, Assets [1] 32,000 20,000 [7]
Total gains (losses) recognized in other comprehensive income, Assets [7]
Purchases/ issues, Assets [2] 80,000 45,000 [7]
Sales/ redemptions, Assets [2] (99,000) (11,000) [7]
Settlements, Assets [7]
Foreign exchange movements, Assets 21,000 (4,000) [7]
Transfers into Level 3, Assets [3],[4] 1,000 0 [7]
Transfers out of Level 3, Assets [4],[5] (2,000) (28,000) [7]
Ending balance, Assets [7],[8] 308,000 275,000
Trading liabilities [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 1,000 1,000
Total gains (losses) recognized in net income, Liabilities [1] (1,000) 0
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 1,000 5,000
Sales/ redemptions, Liabilities [2] (1,000) (5,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 0 0
Transfers into Level 3, Liabilities [3],[4] 0 0
Transfers out of Level 3, Liabilities [4],[5] (1,000) 0
Ending balance, Liabilities 1,000 1,000
Trading liabilities [Member] | Equities [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 1,000 0
Total gains (losses) recognized in net income, Liabilities [1] 0 0
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 0 3,000
Sales/ redemptions, Liabilities [2] 0 (2,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 0 0
Transfers into Level 3, Liabilities [3],[4] 0 0
Transfers out of Level 3, Liabilities [4],[5] (1,000) 0
Ending balance, Liabilities 0 1,000
Trading liabilities [Member] | Bank and corporate debt securities [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 0 1,000
Total gains (losses) recognized in net income, Liabilities [1] 0 0
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 0 2,000
Sales/ redemptions, Liabilities [2] 0 (3,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 0 0
Transfers into Level 3, Liabilities [3],[4] 0 0
Transfers out of Level 3, Liabilities [4],[5] 0 0
Ending balance, Liabilities 0 0
Trading liabilities [Member] | Collateralized debt obligations ("CDOs") and other [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 0 0
Total gains (losses) recognized in net income, Liabilities [1] (1,000)
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 1,000 0
Sales/ redemptions, Liabilities [2] (1,000) 0
Settlements, Liabilities
Foreign exchange movements, Liabilities 0 0
Transfers into Level 3, Liabilities [3],[4]
Transfers out of Level 3, Liabilities [4],[5] 0
Ending balance, Liabilities 1,000 0
Trading liabilities [Member] | Investment trust funds and other [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 0 0
Total gains (losses) recognized in net income, Liabilities [1] 0 0
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 0 0
Sales/ redemptions, Liabilities [2] 0 0
Settlements, Liabilities
Foreign exchange movements, Liabilities 0 0
Transfers into Level 3, Liabilities [3],[4]
Transfers out of Level 3, Liabilities [4],[5]
Ending balance, Liabilities   0
Short-term borrowings [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 36,000 23,000
Total gains (losses) recognized in net income, Liabilities [1] (2,000) (1,000)
Total gains (losses) recognized in other comprehensive income, Liabilities 0 0
Purchases/ issues, Liabilities [2] 96,000 70,000
Sales/ redemptions, Liabilities [2] (79,000) (41,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 2,000 0
Transfers into Level 3, Liabilities [3],[4] 1,000 1,000
Transfers out of Level 3, Liabilities [4],[5] (15,000) (18,000)
Ending balance, Liabilities 43,000 36,000
Payables and deposits [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 14,000 15,000
Total gains (losses) recognized in net income, Liabilities [1] 1,000 1,000
Total gains (losses) recognized in other comprehensive income, Liabilities 0 0
Purchases/ issues, Liabilities [2] 1,000
Sales/ redemptions, Liabilities [2] (1,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities
Transfers into Level 3, Liabilities [3],[4] 1,000
Transfers out of Level 3, Liabilities [4],[5] (2,000)
Ending balance, Liabilities 12,000 14,000
Long-term borrowings [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 477,000 474,000
Total gains (losses) recognized in net income, Liabilities [1] (16,000) 0
Total gains (losses) recognized in other comprehensive income, Liabilities (3,000) 9,000
Purchases/ issues, Liabilities [2] 194,000 218,000
Sales/ redemptions, Liabilities [2] (178,000) (172,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 1,000 0
Transfers into Level 3, Liabilities [3],[4] 21,000 11,000
Transfers out of Level 3, Liabilities [4],[5] (82,000) (45,000)
Ending balance, Liabilities 452,000 477,000
Other liabilities [Member]    
Liabilities [Abstract]    
Beginning balance, Liabilities 65,000 44,000
Total gains (losses) recognized in net income, Liabilities [1] (1,000) 0
Total gains (losses) recognized in other comprehensive income, Liabilities
Purchases/ issues, Liabilities [2] 100,000 47,000
Sales/ redemptions, Liabilities [2] (104,000) (25,000)
Settlements, Liabilities
Foreign exchange movements, Liabilities 5,000 (1,000)
Transfers into Level 3, Liabilities [3],[4] 2,000 0
Transfers out of Level 3, Liabilities [4],[5] (2,000) 0
Ending balance, Liabilities ¥ 67,000 ¥ 65,000
[1] Includes gains and losses reported primarily 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] Amounts reported in Purchases / issues include increases in trading liabilities while Sales / redemptions include decreases in trading liabilities.
[3] Amounts of gains and losses on these transfers which were recognized in the period when the Transfers into Level 3 occurred were not significant for the years ended March 31, 2025 and March 31, 2026.
[4] Transfers into Level 3 indicate certain valuation inputs of a financial instrument become unobservable or significant. Transfers out of Level 3 indicate certain valuation inputs of a financial instrument become observable or insignificant. See “Quantitative and qualitative information regarding significant unobservable valuation inputs” above for the valuation inputs of each financial instruments.
[5] Transfers out of Level 3 include financial instruments that moved out of level 3 by application of measurement alternative. See Note 6 “Non-trading investments” for further information of financial instruments under the measurement alternative.
[6] Derivatives which contain multiple types of risk are classified based on the primary risk type of the instrument.
[7] Includes non-financial assets carried at fair value on a recurring basis.
[8] Valuation techniques and unobservable valuation inputs in respect of equity securities reported within Other assets in the consolidated balance sheets.