v3.26.1
Derivative Financial Instruments and Hedge Accounting - Derivative Financial Instruments by Type and Purpose of Derivatives (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Assets ¥ 10,093,100 ¥ 8,313,016
Liabilities 11,472,444 9,303,258
Trading [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 2,295,916,743 1,908,888,898
Assets 9,199,972 7,539,188
Liabilities 8,620,848 6,765,135
Trading [member] | Interest rate derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 1,973,420,607 1,647,024,810
Assets 4,278,860 4,459,310
Liabilities 5,010,756 4,876,544
Trading [member] | Interest rate derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 98,653,216 89,708,676
Assets 38,078 21,022
Liabilities 40,166 18,155
Trading [member] | Interest rate derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 158,104,302 127,145,993
Assets 29,858 18,358
Liabilities 17,581 22,843
Trading [member] | Interest rate derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 48,904,376 39,526,819
Assets 14,417 258
Liabilities 8,297 1,918
Trading [member] | Interest rate derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 1,355,709,280 1,105,571,439
Assets 3,319,167 3,624,648
Liabilities 3,578,134 3,542,617
Trading [member] | Interest rate derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 312,049,433 285,071,883
Assets 877,340 795,024
Liabilities 1,366,578 1,291,011
Trading [member] | Currency derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 315,106,852 255,610,108
Assets 4,792,354 2,888,987
Liabilities 3,494,996 1,827,299
Trading [member] | Currency derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 47,899 12,976
Assets  
Liabilities 2,160 94
Trading [member] | Currency derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Trading [member] | Currency derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 146,585,047 119,480,108
Assets 1,690,794 935,964
Liabilities 1,591,981 1,103,594
Trading [member] | Currency derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 148,252,146 123,676,347
Assets 2,858,275 1,754,071
Liabilities 1,543,672 479,671
Trading [member] | Currency derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 20,221,760 12,440,677
Assets 243,285 198,952
Liabilities 357,183 243,940
Trading [member] | Equity derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 2,628,133 2,729,785
Assets 67,937 161,801
Liabilities 45,616 22,092
Trading [member] | Equity derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 2,113,484 1,882,834
Assets 55,834 28,003
Liabilities 31,025 10,533
Trading [member] | Equity derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 253,138 332,227
Assets 6,185 5,406
Liabilities 10,003 8,462
Trading [member] | Equity derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 26,803 250,439
Assets 563 119,372
Liabilities 796 180
Trading [member] | Equity derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 64,321 36,576
Assets 964 694
Liabilities 2,259 225
Trading [member] | Equity derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 170,387 227,709
Assets 4,391 8,326
Liabilities 1,533 2,692
Trading [member] | Commodity derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 276,602 175,113
Assets 34,909 5,652
Liabilities 33,753 4,384
Trading [member] | Commodity derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 126,273 85,473
Assets 10,815 1,807
Liabilities 9,371 1,796
Trading [member] | Commodity derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Trading [member] | Commodity derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Trading [member] | Commodity derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 142,213 84,608
Assets 24,094 3,771
Liabilities 23,582 2,525
Trading [member] | Commodity derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 8,116 5,032
Assets 74
Liabilities 800 63
Trading [member] | Credit derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 4,484,549 3,349,082
Assets 25,912 23,438
Liabilities 35,727 34,816
Risk management [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 103,019,620 104,751,735
Assets 893,128 773,828
Liabilities 2,851,596 2,538,123
Risk management [member] | Interest rate derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 82,693,098 82,319,161
Assets 726,570 610,989
Liabilities 926,053 904,337
Risk management [member] | Interest rate derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 2,403,589 10,784,613
Assets 979
Liabilities 1,594 11,420
Risk management [member] | Interest rate derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Interest rate derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Interest rate derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 80,003,146 71,326,701
Assets 725,860 610,010
Liabilities 885,290 857,991
Risk management [member] | Interest rate derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 286,363 207,847
Assets 710  
Liabilities 39,169 34,926
Risk management [member] | Currency derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 20,326,522 22,432,574
Assets 166,558 162,839
Liabilities 1,925,543 1,633,786
Risk management [member] | Currency derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Currency derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Currency derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 8,349,254 8,511,080
Assets 80,718 57,888
Liabilities 311,523 153,892
Risk management [member] | Currency derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts 11,977,268 13,921,494
Assets 85,840 104,951
Liabilities 1,614,020 ¥ 1,479,894
Risk management [member] | Currency derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Equity derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member] | Futures [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member] | Listed options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member] | Forwards [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member] | Swaps [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Commodity derivatives [member] | OTC options [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities  
Risk management [member] | Credit derivatives [member]    
Disclosure of detailed information about financial instruments [line items]    
Notional amounts  
Assets  
Liabilities