v3.26.1
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
Mar. 31, 2026
Mar. 31, 2025
Japanese and foreign government bond securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value ¥ 69,055 ¥ 132,283
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (11,720) (9,785)
Available-for-sale debt Securities, 12 months or more Fair value 897,208 913,742
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (666,371) (419,686)
Available-for-sale debt Securities, Total Fair value 966,263 1,046,025
Available-for-sale debt Securities, Total Gross unrealized losses (678,091) (429,471)
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 69,055 132,283
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (11,720) (9,785)
Available-for-sale debt Securities, 12 months or more Fair value 897,208 913,742
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (666,371) (419,686)
Available-for-sale debt Securities, Total Fair value 966,263 1,046,025
Available-for-sale debt Securities, Total Gross unrealized losses (678,091) (429,471)
Japanese prefectural and foreign municipal bond securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 76,347 95,936
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (3,270) (3,409)
Available-for-sale debt Securities, 12 months or more Fair value 138,277 224,679
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (39,327) (31,734)
Available-for-sale debt Securities, Total Fair value 214,624 320,615
Available-for-sale debt Securities, Total Gross unrealized losses (42,597) (35,143)
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 75,944 94,691
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (2,735) (3,325)
Available-for-sale debt Securities, 12 months or more Fair value 133,042 220,950
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (39,064) (31,573)
Available-for-sale debt Securities, Total Fair value 208,986 315,641
Available-for-sale debt Securities, Total Gross unrealized losses (41,799) (34,898)
Corporate debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 128,382 152,094
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (4,467) (5,196)
Available-for-sale debt Securities, 12 months or more Fair value 536,002 427,837
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (173,551) (113,802)
Available-for-sale debt Securities, Total Fair value 664,384 579,931
Available-for-sale debt Securities, Total Gross unrealized losses (178,018) (118,998)
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 122,570 149,367
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (4,347) (5,128)
Available-for-sale debt Securities, 12 months or more Fair value 536,002 427,837
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (173,551) (113,802)
Available-for-sale debt Securities, Total Fair value 658,572 577,204
Available-for-sale debt Securities, Total Gross unrealized losses (177,898) (118,930)
CMBS and RMBS in the Americas    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 38,338 16,940
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (300) (103)
Available-for-sale debt Securities, 12 months or more Fair value 10,930 15,817
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (2,184) (777)
Available-for-sale debt Securities, Total Fair value 49,268 32,757
Available-for-sale debt Securities, Total Gross unrealized losses (2,484) (880)
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 38,338 16,940
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (300) (103)
Available-for-sale debt Securities, 12 months or more Fair value 10,930 15,817
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (257) (777)
Available-for-sale debt Securities, Total Fair value 49,268 32,757
Available-for-sale debt Securities, Total Gross unrealized losses (557) (880)
Other asset-backed securities and debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 44,823 56,671
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (1,499) (411)
Available-for-sale debt Securities, 12 months or more Fair value 35,603 35,183
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (11,287) (6,966)
Available-for-sale debt Securities, Total Fair value 80,426 91,854
Available-for-sale debt Securities, Total Gross unrealized losses (12,786) (7,377)
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 44,796 56,671
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (1,319) (340)
Available-for-sale debt Securities, 12 months or more Fair value 34,484 34,868
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (10,583) (6,553)
Available-for-sale debt Securities, Total Fair value 79,280 91,539
Available-for-sale debt Securities, Total Gross unrealized losses (11,902) (6,893)
Available-for-sale debt securities    
Investments, Unrealized Loss Position [Line Items]    
Available-for-sale debt Securities, Less than 12 months Fair value 356,945 453,924
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (21,256) (18,904)
Available-for-sale debt Securities, 12 months or more Fair value 1,618,020 1,617,258
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (892,720) (572,965)
Available-for-sale debt Securities, Total Fair value 1,974,965 2,071,182
Available-for-sale debt Securities, Total Gross unrealized losses (913,976) (591,869)
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 350,703 449,952
Available-for-sale debt Securities, Less than 12 months Gross unrealized losses (20,421) (18,681)
Available-for-sale debt Securities, 12 months or more Fair value 1,611,666 1,613,214
Available-for-sale debt Securities, 12 months or more Gross unrealized losses (889,826) (572,391)
Available-for-sale debt Securities, Total Fair value 1,962,369 2,063,166
Available-for-sale debt Securities, Total Gross unrealized losses ¥ (910,247) ¥ (591,072)