Investments - Gross Unrealized Losses and Fair Value of Available-for-Sale and Held-to-Maturity Securities, Aggregated by Length of Time that Individual Securities Have Been in a Continuous Unrealized Loss Position (Parenthetical) (Detail) - JPY (¥)
¥ in Millions

Mar. 31, 2026

Mar. 31, 2025

Gain (Loss) on Securities [Line Items]

Fair value, available-for-sale securities

¥ 17,658,445

¥ 11,011,377

Debt securities | Agency mortgage-backed securities

Gain (Loss) on Securities [Line Items]

Fair value, available-for-sale securities

^[1]

281,815

308,626

Debt securities | Japanese agency mortgage-backed securities | Agency mortgage-backed securities

Gain (Loss) on Securities [Line Items]

Fair value, available-for-sale securities

¥ 281,815

¥ 308,626

[1]

Agency mortgage-backed securities presented in this line consist of Japanese agency mortgage-backed securities, of which the fair values were ¥308,626 million at March 31, 2025, and ¥281,815 million at March 31, 2026. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.