v3.26.1
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings (Secured Borrowing by the Class of Collateral Pledged) (Detail) - JPY (¥)
¥ in Billions
Mar. 31, 2026
Mar. 31, 2025
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements ¥ 42,292 ¥ 46,381
Payables under securities lending transactions 1,252 737
Obligations to return securities received as collateral 8,468 6,047
Total 52,012 53,165
Japanese national government and Japanese government agency bonds    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 9,738 16,652
Payables under securities lending transactions 560 165
Obligations to return securities received as collateral 3,196 3,438
Total 13,494 20,255
Foreign government and official institution bonds    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 22,887 16,955
Payables under securities lending transactions 11 30
Obligations to return securities received as collateral 1,981 917
Total 24,879 17,902
Corporate bonds    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 992 1,012
Payables under securities lending transactions 0 0
Obligations to return securities received as collateral 442 358
Total 1,434 1,370
Residential mortgage-backed securities    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 6,990 10,695
Payables under securities lending transactions 0 0
Obligations to return securities received as collateral 6 0
Total 6,996 10,695
Other debt securities    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 360 190
Payables under securities lending transactions 0 0
Obligations to return securities received as collateral 3 2
Total 363 192
Marketable equity securities    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 1,315 846
Payables under securities lending transactions 640 531
Obligations to return securities received as collateral 2,840 1,332
Total 4,795 2,709
Other    
Repurchase Agreements, and Securities Lending Transactions Accounted for as Secured Borrowings [Line Items]    
Payables under repurchase agreements 10 31
Payables under securities lending transactions 41 11
Obligations to return securities received as collateral 0 0
Total ¥ 51 ¥ 42