v3.26.1
Securitizations and Variable Interest Entities - Fair value of retained interests (Detail) - JPY (¥)
¥ in Billions
Mar. 31, 2026
Mar. 31, 2025
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests ¥ 208 ¥ 250
Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 192 241
Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 16 9
Investment grade [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 192 243
Investment grade [Member] | Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 192 241
Investment grade [Member] | Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Investment grade [Member] | CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests   2
Other [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 16 7
Other [Member] | Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Other [Member] | Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Other [Member] | CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 16 7
Level 1 [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 1 [Member] | Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 1 [Member] | Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 1 [Member] | CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 2 [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 192 241
Level 2 [Member] | Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 192 241
Level 2 [Member] | Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 2 [Member] | CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 3 [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests 16 9
Level 3 [Member] | Government, agency and municipal securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 3 [Member] | Bank and corporate debt securities [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests
Level 3 [Member] | CMBS and RMBS [Member]    
Schedule of fair value of retained interests [Line Items]    
Fair value of retained interests ¥ 16 ¥ 9