v3.26.1
Equity Method Investments (Summary of Information Relating to The Equity Method Investees) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Operations:      
Total revenues ¥ 3,330,831 ¥ 2,874,821 ¥ 2,814,361
Financial position:      
Total assets 18,002,776 16,866,251 16,322,100
Total liabilities 13,378,965 12,691,036  
Total equity 4,482,500 4,089,782  
TB Investment Limited Partnership [Member]      
Operations:      
Total revenues 3,558,900 3,506,193 759,042
Income before income taxes 613,324 174,744 (76,343)
Net income 340,103 76,819 (70,020)
Financial position:      
Total assets 4,839,652 4,694,585 4,429,618
Total liabilities 3,331,150 3,652,131 3,157,087
Total equity 1,508,502 1,042,454 1,272,531
Equity Method Investment, Nonconsolidated Investee, Other [Member]      
Operations:      
Total revenues 2,215,250 2,293,309 2,112,692
Income before income taxes 743,907 432,759 343,309
Net income 674,849 343,938 268,026
Financial position:      
Total assets 22,236,185 23,580,665 22,259,744
Total liabilities 13,678,221 15,209,476 14,021,875
Total equity ¥ 8,557,964 ¥ 8,371,189 ¥ 8,237,869