v3.26.3
Investment in Securities (Information about Available-for-Sale and Held-to-Maturity Securities with Gross Unrealized Losses and Length of Time that Individual Securities Have Been in Continuous Unrealized Loss Position) (Detail) - JPY (¥)
¥ in Millions
Sep. 30, 2026
Mar. 31, 2026
Japanese and foreign government bond securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value ¥ 35,033 ¥ 63,108
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (7,978) (11,483)
Available-for-sale debt Securities, 12 months or more Fair value 873,877 897,208
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (764,638) (666,371)
Available-for-sale debt Securities, Total Fair value 908,910 960,316
Available-for-sale debt Securities, Total Gross unrealized losses (772,616) (677,854)
Japanese and foreign government bond securities | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 35,033 63,108
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (7,978) (11,483)
Available-for-sale debt Securities, 12 months or more Fair value 873,877 897,208
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (764,638) (666,371)
Available-for-sale debt Securities, Total Fair value 908,910 960,316
Available-for-sale debt Securities, Total Gross unrealized losses (772,616) (677,854)
Japanese prefectural and foreign municipal bond securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 130,988 23,916
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (9,450) (1,312)
Available-for-sale debt Securities, 12 months or more Fair value 94,159 114,487
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (42,513) (37,217)
Available-for-sale debt Securities, Total Fair value 225,147 138,403
Available-for-sale debt Securities, Total Gross unrealized losses (51,963) (38,529)
Japanese prefectural and foreign municipal bond securities | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 130,865 23,513
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (8,923) (777)
Available-for-sale debt Securities, 12 months or more Fair value 92,986 109,252
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (42,425) (36,954)
Available-for-sale debt Securities, Total Fair value 223,851 132,765
Available-for-sale debt Securities, Total Gross unrealized losses (51,348) (37,731)
Corporate debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 363,166 117,908
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (32,276) (4,162)
Available-for-sale debt Securities, 12 months or more Fair value 334,155 477,946
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (184,195) (172,153)
Available-for-sale debt Securities, Total Fair value 697,321 595,854
Available-for-sale debt Securities, Total Gross unrealized losses (216,471) (176,315)
Corporate debt securities | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 352,131 112,096
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (31,996) (4,042)
Available-for-sale debt Securities, 12 months or more Fair value 334,155 477,946
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (184,195) (172,153)
Available-for-sale debt Securities, Total Fair value 686,286 590,042
Available-for-sale debt Securities, Total Gross unrealized losses (216,191) (176,195)
CMBS and RMBS in the Americas    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 55,991 38,338
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (815) (300)
Available-for-sale debt Securities, 12 months or more Fair value 4,789 10,930
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (2,095) (2,184)
Available-for-sale debt Securities, Total Fair value 60,780 49,268
Available-for-sale debt Securities, Total Gross unrealized losses (2,910) (2,484)
CMBS and RMBS in the Americas | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 55,991 38,338
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (815) (300)
Available-for-sale debt Securities, 12 months or more Fair value 4,789 10,930
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (199) (257)
Available-for-sale debt Securities, Total Fair value 60,780 49,268
Available-for-sale debt Securities, Total Gross unrealized losses (1,014) (557)
Other asset-backed securities and debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 38,979 43,230
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (1,518) (1,492)
Available-for-sale debt Securities, 12 months or more Fair value 35,512 33,573
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (10,455) (10,673)
Available-for-sale debt Securities, Total Fair value 74,491 76,803
Available-for-sale debt Securities, Total Gross unrealized losses (11,973) (12,165)
Other asset-backed securities and debt securities | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 37,859 43,203
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (997) (1,312)
Available-for-sale debt Securities, 12 months or more Fair value 35,431 32,454
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (10,221) (9,969)
Available-for-sale debt Securities, Total Fair value 73,290 75,657
Available-for-sale debt Securities, Total Gross unrealized losses (11,218) (11,281)
Available-for-sale debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 624,157 286,500
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (52,037) (18,749)
Available-for-sale debt Securities, 12 months or more Fair value 1,342,492 1,534,144
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (1,003,896) (888,598)
Available-for-sale debt Securities, Total Fair value 1,966,649 1,820,644
Available-for-sale debt Securities, Total Gross unrealized losses (1,055,933) (907,347)
Available-for-sale debt securities | Allowance for credit losses not recorded    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 611,879 280,258
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (50,709) (17,914)
Available-for-sale debt Securities, 12 months or more Fair value 1,341,238 1,527,790
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (1,001,678) (885,704)
Available-for-sale debt Securities, Total Fair value 1,953,117 1,808,048
Available-for-sale debt Securities, Total Gross unrealized losses ¥ (1,052,387) ¥ (903,618)