v3.26.1
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
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost ¥ 3,403,138 ¥ 3,174,036  
Available-for-sale debt securities, Allowance for credit losses (3,505) (670) ¥ (634)
Available-for-sale debt securities, Gross unrealized gains 37,254 25,470  
Available-for-sale debt securities, Gross unrealized losses (910,471) (591,199)  
Available-for-sale debt securities, Fair value 2,526,416 2,607,637  
Japanese and foreign government bond securities      
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost 1,651,782 1,520,672  
Available-for-sale debt securities, Allowance for credit losses 0 0  
Available-for-sale debt securities, Gross unrealized gains 194 1,325  
Available-for-sale debt securities, Gross unrealized losses (678,091) (429,471)  
Available-for-sale debt securities, Fair value 973,885 1,092,526  
Japanese prefectural and foreign municipal bond securities      
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost 352,338 439,565  
Available-for-sale debt securities, Allowance for credit losses (798) (245)  
Available-for-sale debt securities, Gross unrealized gains 6,025 2,408  
Available-for-sale debt securities, Gross unrealized losses (41,799) (34,898)  
Available-for-sale debt securities, Fair value 315,766 406,830  
Corporate debt securities      
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost 1,110,521 906,297  
Available-for-sale debt securities, Allowance for credit losses (64) (34)  
Available-for-sale debt securities, Gross unrealized gains 24,946 15,246  
Available-for-sale debt securities, Gross unrealized losses (177,954) (118,964)  
Available-for-sale debt securities, Fair value 957,449 802,545  
CMBS and RMBS in the Americas      
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost 107,361 106,578  
Available-for-sale debt securities, Allowance for credit losses (1,927) 0  
Available-for-sale debt securities, Gross unrealized gains 555 1,053  
Available-for-sale debt securities, Gross unrealized losses (557) (880)  
Available-for-sale debt securities, Fair value 105,432 106,751  
Other asset-backed securities and debt securities      
Schedule of Investments [Line Items]      
Available-for-sale debt securities, Amortized cost 181,136 200,924  
Available-for-sale debt securities, Allowance for credit losses (716) (391)  
Available-for-sale debt securities, Gross unrealized gains 5,534 5,438  
Available-for-sale debt securities, Gross unrealized losses (12,070) (6,986)  
Available-for-sale debt securities, Fair value ¥ 173,884 ¥ 198,985