v3.25.2
Fair Value (Quantitative Information about Level 3 Fair Value Measurements) (Detail) - Fair value, recurring measurements - Level 3
¥ in Millions
Mar. 31, 2025
JPY (¥)
Mar. 31, 2024
JPY (¥)
Interest rate contracts | Option model    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Fair value ¥ (21,934) ¥ 41,687
Interest rate contracts | Option model | Recovery rate | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.800  
Interest rate contracts | Option model | Recovery rate | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.900  
Interest rate contracts | Option model | Recovery rate | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.850  
Interest rate contracts | Option model | Correlation between interest rates | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.300 0.300
Interest rate contracts | Option model | Correlation between interest rates | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.604 0.607
Interest rate contracts | Option model | Correlation between interest rates | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.440 0.446
Interest rate contracts | Option model | Correlation between interest rate and foreign exchange rate | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.057 (0.020)
Interest rate contracts | Option model | Correlation between interest rate and foreign exchange rate | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.600 0.600
Interest rate contracts | Option model | Correlation between interest rate and foreign exchange rate | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.343 0.350
Interest rate contracts | Option model | Volatility | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.653 0.612
Interest rate contracts | Option model | Volatility | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 1.346 0.806
Interest rate contracts | Option model | Volatility | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.735 0.756
Foreign exchange contracts | Option model    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Fair value ¥ 25,319 ¥ 9,800
Foreign exchange contracts | Option model | Recovery rate | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.800  
Foreign exchange contracts | Option model | Recovery rate | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.900  
Foreign exchange contracts | Option model | Recovery rate | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.850  
Foreign exchange contracts | Option model | Correlation between interest rates | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.300 0.300
Foreign exchange contracts | Option model | Correlation between interest rates | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.700 0.700
Foreign exchange contracts | Option model | Correlation between interest rates | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.456 0.482
Foreign exchange contracts | Option model | Correlation between interest rate and foreign exchange rate | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.192 0.176
Foreign exchange contracts | Option model | Correlation between interest rate and foreign exchange rate | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.600 0.600
Foreign exchange contracts | Option model | Correlation between interest rate and foreign exchange rate | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.367 0.363
Foreign exchange contracts | Option model | Volatility | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.107 0.099
Foreign exchange contracts | Option model | Volatility | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.209 0.213
Foreign exchange contracts | Option model | Volatility | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.143 0.141
Foreign exchange contracts | Option model | Correlation between foreign exchange rates | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.500 0.500
Foreign exchange contracts | Option model | Correlation between foreign exchange rates | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.664 0.706
Foreign exchange contracts | Option model | Correlation between foreign exchange rates | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.582 0.664
Equity contracts | Option model    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Fair value ¥ 3,524 ¥ 4,414
Equity contracts | Option model | Volatility | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.200 0.250
Equity contracts | Option model | Volatility | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.355 0.370
Equity contracts | Option model | Volatility | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.275 0.339
Equity contracts | Option model | Correlation between foreign exchange rate and equity | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.060 0.000
Equity contracts | Option model | Correlation between foreign exchange rate and equity | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.500 0.300
Equity contracts | Option model | Correlation between foreign exchange rate and equity | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.100 0.200
Equity contracts | Option model | Correlation between equities | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.057 0.050
Equity contracts | Option model | Correlation between equities | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.950 0.760
Equity contracts | Option model | Correlation between equities | Median    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading derivatives—net, Significant unobservable inputs 0.589 0.575
Asset-backed securities | Internal model    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Fair value ¥ 1,684,080 ¥ 1,248,241
Asset-backed securities | Internal model | Asset correlations    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.020 0.030
Asset-backed securities | Internal model | Asset correlations | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.020 0.030
Asset-backed securities | Internal model | Discount factor | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.012 0.014
Asset-backed securities | Internal model | Discount factor | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.013 0.016
Asset-backed securities | Internal model | Discount factor | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.013 0.014
Asset-backed securities | Internal model | Prepayment rate    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.280 0.177
Asset-backed securities | Internal model | Prepayment rate | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.280 0.177
Asset-backed securities | Internal model | Probability of default | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.000 0.000
Asset-backed securities | Internal model | Probability of default | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.990 0.930
Asset-backed securities | Internal model | Probability of default | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0 0
Asset-backed securities | Internal model | Recovery rate    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.604 0.550
Asset-backed securities | Internal model | Recovery rate | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.604 0.550
Other debt securities | Discounted cash flow    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Fair value ¥ 659,534 ¥ 587,272
Other debt securities | Discounted cash flow | Liquidity premium | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.016 0.009
Other debt securities | Discounted cash flow | Liquidity premium | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.032 0.032
Other debt securities | Discounted cash flow | Liquidity premium | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.024 0.028
Corporate bonds | Discounted cash flow    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Fair value ¥ 175,464  
Corporate bonds | Discounted cash flow | Liquidity premium | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.000  
Corporate bonds | Discounted cash flow | Liquidity premium | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.002  
Corporate bonds | Discounted cash flow | Liquidity premium | Weighted average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Trading securities and Investment securities, Significant unobservable inputs 0.001