v3.25.2
Fair Value (Gains (Losses) Related to Instruments for which Fair Value Option was Elected) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Financial liabilities:      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value ¥ 13,952 ¥ (16,736) ¥ 37,318
Financial liabilities: | Trading account profits (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 13,952 (16,736) 37,318
Financial liabilities: | Foreign exchange gains (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 0 0 0
Financial liabilities: | Other short-term borrowings      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 3,832 3,690 (3,626)
Financial liabilities: | Other short-term borrowings | Trading account profits (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 3,832 3,690 (3,626)
Financial liabilities: | Other short-term borrowings | Foreign exchange gains (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 0 0 0
Financial liabilities: | Long-term debt      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 10,120 (20,426) 40,944
Financial liabilities: | Long-term debt | Trading account profits (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 10,120 (20,426) 40,944
Financial liabilities: | Long-term debt | Foreign exchange gains (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 0 0 0
Financial assets:      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 40,037 2,003,099 188,760
Financial assets: | Trading account profits (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 1,636 (173,290) (1,180,311)
Financial assets: | Foreign exchange gains (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 38,401 2,176,389 1,369,071
Financial assets: | Trading account securities      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 40,037 2,003,099 188,760
Financial assets: | Trading account securities | Trading account profits (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value 1,636 (173,290) (1,180,311)
Financial assets: | Trading account securities | Foreign exchange gains (losses)      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Gains (Losses) on changes in fair value ¥ 38,401 ¥ 2,176,389 ¥ 1,369,071