v3.26.1
Repurchase Agreements and Securities Lending Transactions Accounted for as Secured Borrowings (Gross Amounts of Liabilities by Class of Underlying Collateral) (Detail) - JPY (¥)
¥ in Billions
Mar. 31, 2026
Mar. 31, 2025
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements [1] ¥ 37,732 ¥ 38,395
Securities lending transactions [1] 2,067 1,675
Japanese government bonds and Japanese local government bonds    
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements 6,276 6,556
Securities lending transactions 15 77
Foreign government bonds and foreign agency mortgage-backed securities    
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements 27,984 29,467
Securities lending transactions 252 302
Commercial Paper and Corporate Bonds    
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements 835 734
Securities lending transactions 0 0
Equity Securities    
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements 989 902
Securities lending transactions 1,801 1,296
Other    
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]    
Repurchase agreements 1,648 736
Securities lending transactions ¥ 0 ¥ 0
[1] The above table does not include securities-for-securities lending transactions of ¥125 billion at March 31, 2025 and ¥—  billion at March 31, 2026, where the MHFG Group acts as lender and receives securities that can be sold or pledged as collateral. In these transactions, the Group recognizes the securities received at fair value within Other assets and the obligation to return those securities as a liability within Other liabilities.