v3.26.1
Securitizations and Variable Interest Entities - Carrying amount of variable interests of unconsolidated VIEs and maximum exposure to loss (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets ¥ 62,645,925 ¥ 56,802,170
Carrying amount of variable interests, Liabilities 58,791,010 53,221,171
Variable Interest Entity, Not Primary Beneficiary [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 5,337,000 5,278,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 5,525,000 5,445,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Equities [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 23,000 23,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 23,000 23,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Debt securities [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 63,000 80,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 63,000 80,000
Variable Interest Entity, Not Primary Beneficiary [Member] | CMBS and RMBS [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 2,807,000 3,288,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 2,807,000 3,288,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Investment trust funds and other [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 187,000 129,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 187,000 129,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Private equity and debt investments [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 20,000 23,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 20,000 23,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Loans [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 2,205,000 1,712,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 2,205,000 1,712,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Other [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets 32,000 23,000
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs 32,000 23,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Commitments to extend credit and other guarantees [Member]    
Variable Interest Entity [Line Items]    
Carrying amount of variable interests, Assets
Carrying amount of variable interests, Liabilities
Maximum exposure to loss to unconsolidated VIEs ¥ 188,000 ¥ 167,000