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Investments - Summary of Details of Net Gains and Losses on Equity Securities (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Gain (Loss) on Securities [Line Items]      
Net gains (losses) recognized during the period on equity securities [1] ¥ 1,035,589 ¥ (181,948) ¥ 1,010,288
Less: Net gains (losses) recognized during the period on equity securities sold during the period 243,035 72,627 235,564
Unrealized gains (losses) recognized during the reporting period on equity securities still held at the reporting period ¥ 792,553 ¥ (254,575) ¥ 774,724
[1] These amounts are revenues from contracts that do not meet the scope of ASC 606.