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Trading Account Profits and Losses (Net Trading Gains (Losses)) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Trading Account Profits And Losses [Abstract]      
Interest rate and other derivative contracts ¥ (1,703,103) ¥ (95,783) ¥ (951,913)
Trading account securities, excluding derivatives 1,052,530 128,045 248,000
Trading account profits (losses)—net (650,573) 32,262 (703,913)
Foreign exchange derivative contracts (760,095) 446,992 (410,656)
Net trading profits (losses) ¥ (1,410,668) ¥ 479,254 ¥ (1,114,569)