v3.26.1
Derivative instruments and hedging activities - Schedule of information about written credit derivatives by external credit rating of underlying asset (Detail) - JPY (¥)
¥ in Billions
Mar. 31, 2026
Mar. 31, 2025
Credit Derivatives [Line Items]    
Maximum potential payout / Notional ¥ 68,210 ¥ 28,375
Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 23,468 11,480
Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 42,499 15,488
Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 1,824 1,236
Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 419 171
AAA [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 179 603
AAA [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 133 571
AAA [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 46 32
AAA [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional
AAA [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional
AA [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 5,728 1,893
AA [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 2,999 1,855
AA [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 2,702 38
AA [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 13
AA [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 14
A [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 13,920 7,470
A [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 7,182 3,488
A [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 6,605 3,958
A [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 3 24
A [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 130
BBB [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 30,044 15,344
BBB [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 9,459 4,213
BBB [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 19,626 10,256
BBB [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 959 748
BBB [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 127
BB [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 3,155 952
BB [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 2,406 655
BB [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 720 277
BB [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 27 20
BB [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional 2
Other [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional [1] 15,184 2,113
Other [Member] | Single-name credit default swaps [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional [1] 1,289 698
Other [Member] | Credit default swap indices [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional [1] 12,800 927
Other [Member] | Other credit risk-related portfolio products [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional [1] 822 444
Other [Member] | Credit risk-related options and swaptions [Member]    
Credit Derivatives [Line Items]    
Maximum potential payout / Notional [1] ¥ 273 ¥ 44
[1] Other includes credit derivatives where the credit rating of the underlying reference asset is below investment grade or where a credit rating is unavailable.