v3.26.3
Investment in Securities (Amortized Cost Basis Amounts, Gross Unrealized Holding Gains, Gross Unrealized Holding Losses and Fair Values of Available-for-Sale Securities and Held-to-Maturity Securities in Each Major Security Type) (Detail) - JPY (¥)
¥ in Millions
Sep. 30, 2026
Mar. 31, 2026
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost ¥ 3,368,877 ¥ 3,230,567
Available-for-sale debt securities, allowance for credit losses (3,354) (3,505)
Available-for-sale debt securities, Gross unrealized gains 20,460 37,141
Available-for-sale debt securities, Gross unrealized losses (1,052,579) (903,842)
Available-for-sale debt securities, Fair value 2,333,404 2,360,361
Japanese and foreign government bond securities    
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost 1,700,202 1,645,596
Available-for-sale debt securities, allowance for credit losses 0 0
Available-for-sale debt securities, Gross unrealized gains 0 195
Available-for-sale debt securities, Gross unrealized losses (772,616) (677,854)
Available-for-sale debt securities, Fair value 927,586 967,937
Japanese prefectural and foreign municipal bond securities    
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost 321,116 272,050
Available-for-sale debt securities, allowance for credit losses (615) (798)
Available-for-sale debt securities, Gross unrealized gains 2,930 6,024
Available-for-sale debt securities, Gross unrealized losses (51,348) (37,731)
Available-for-sale debt securities, Fair value 272,083 239,545
Corporate debt securities    
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost 1,071,648 1,040,288
Available-for-sale debt securities, allowance for credit losses (143) (64)
Available-for-sale debt securities, Gross unrealized gains 12,513 24,946
Available-for-sale debt securities, Gross unrealized losses (216,328) (176,251)
Available-for-sale debt securities, Fair value 867,690 888,919
CMBS and RMBS in the Americas    
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost 108,037 107,361
Available-for-sale debt securities, allowance for credit losses (1,896) (1,927)
Available-for-sale debt securities, Gross unrealized gains 558 555
Available-for-sale debt securities, Gross unrealized losses (1,014) (557)
Available-for-sale debt securities, Fair value 105,685 105,432
Other asset-backed securities and debt securities    
Schedule of Investments [Line Items]    
Available-for-sale debt securities, Amortized cost 167,874 165,272
Available-for-sale debt securities, allowance for credit losses (700) (716)
Available-for-sale debt securities, Gross unrealized gains 4,459 5,421
Available-for-sale debt securities, Gross unrealized losses (11,273) (11,449)
Available-for-sale debt securities, Fair value ¥ 160,360 ¥ 158,528