v3.26.3
Investment in Securities (Summary of Investment in Securities) (Parenthetical) (Detail) - JPY (¥)
¥ in Millions
Sep. 30, 2026
Mar. 31, 2026
Schedule of Investments [Line Items]    
Equity securities ¥ 51,788 ¥ 39,796
Equity securities [1] 639,339 782,137
Investment Funds Elected for Fair Value Option    
Schedule of Investments [Line Items]    
Equity securities 25,231 24,845
Variable Annuity and Variable Life Insurance Contracts    
Schedule of Investments [Line Items]    
Equity securities ¥ 146,898 ¥ 137,933
[1] The amount of assets under management of variable annuity and variable life insurance contracts included in equity securities were ¥137,933 million and ¥146,898 million as of March 31, 2026 and September 30, 2026, respectively. The amount of investment funds that elected the fair value option and were included in equity securities were ¥24,845 million and ¥25,231 million as of March 31, 2026 and September 30, 2026, respectively.