v3.26.1
Investments - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Schedule of Investments [Line Items]    
Gross unrealized losses, available-for-sale securities ¥ 140,927 ¥ 82,211
Fair value, available-for-sale securities 21,848,687 15,058,617
Amortized cost, held-to-maturity securities 4,852,384 4,185,763
Total 4,711,064  
Available-for-sale securities | Debt securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 21,971,727 15,114,585
Gross unrealized gains, available-for-sale securities 17,887 26,243
Gross unrealized losses, available-for-sale securities 140,927 82,211
Fair value, available-for-sale securities 21,848,687 15,058,617
Available-for-sale securities | Debt securities | Japanese government bonds    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 14,977,828 8,378,639
Gross unrealized gains, available-for-sale securities 32 123
Gross unrealized losses, available-for-sale securities 52,939 16,329
Fair value, available-for-sale securities 14,924,920 8,362,432
Available-for-sale securities | Debt securities | Japanese local government bonds    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 157,569 571,110
Gross unrealized gains, available-for-sale securities 1 5
Gross unrealized losses, available-for-sale securities 7,869 23,376
Fair value, available-for-sale securities 149,702 547,739
Available-for-sale securities | Debt securities | U.S. Treasury bonds and federal agency securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 137,811 127,719
Gross unrealized gains, available-for-sale securities 186 34
Gross unrealized losses, available-for-sale securities 25 123
Fair value, available-for-sale securities 137,973 127,630
Available-for-sale securities | Debt securities | Other foreign government bonds    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 3,562,809 2,586,790
Gross unrealized gains, available-for-sale securities 4,412 6,078
Gross unrealized losses, available-for-sale securities 3,263 1,704
Fair value, available-for-sale securities 3,563,958 2,591,164
Available-for-sale securities | Debt securities | Agency mortgage-backed securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2],[3] 342,743 340,583
Gross unrealized gains, available-for-sale securities [3] 0 10
Gross unrealized losses, available-for-sale securities [3] 60,907 25,034
Fair value, available-for-sale securities [3] 281,835 315,558
Available-for-sale securities | Debt securities | Residential mortgage-backed securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 11,794 21,802
Gross unrealized gains, available-for-sale securities 0 1
Gross unrealized losses, available-for-sale securities 0 897
Fair value, available-for-sale securities 11,794 20,907
Available-for-sale securities | Debt securities | Commercial mortgage-backed securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 912,841 850,518
Gross unrealized gains, available-for-sale securities 4,040 4,693
Gross unrealized losses, available-for-sale securities 2,870 1,424
Fair value, available-for-sale securities 914,012 853,787
Available-for-sale securities | Debt securities | Japanese corporate bonds and other debt securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2] 926,093 1,436,823
Gross unrealized gains, available-for-sale securities 8,357 13,220
Gross unrealized losses, available-for-sale securities 11,722 11,952
Fair value, available-for-sale securities 922,727 1,438,091
Available-for-sale securities | Debt securities | Foreign corporate bonds and other debt securities    
Schedule of Investments [Line Items]    
Amortized cost, net available-for-sale securities [1],[2],[4] 942,239 800,601
Gross unrealized gains, available-for-sale securities [4] 860 2,079
Gross unrealized losses, available-for-sale securities [4] 1,332 1,371
Fair value, available-for-sale securities [4] 941,766 801,309
Held-to-maturity Securities | Debt securities    
Schedule of Investments [Line Items]    
Amortized cost, held-to-maturity securities [1],[2] 4,852,384 4,185,763
Gross unrealized gains, held-to-maturity securities 36,938 23,982
Gross unrealized losses, held-to-maturity securities 178,258 182,364
Total 4,711,064 4,027,381
Held-to-maturity Securities | Debt securities | Japanese government bonds    
Schedule of Investments [Line Items]    
Amortized cost, held-to-maturity securities [1],[2] 419,568 419,480
Gross unrealized gains, held-to-maturity securities 0 0
Gross unrealized losses, held-to-maturity securities 26,355 19,601
Total 393,213 399,879
Held-to-maturity Securities | Debt securities | Agency mortgage-backed securities    
Schedule of Investments [Line Items]    
Amortized cost, held-to-maturity securities [1],[2],[5] 4,432,816 3,766,283
Gross unrealized gains, held-to-maturity securities [5] 36,938 23,982
Gross unrealized losses, held-to-maturity securities [5] 151,903 162,763
Total [5] ¥ 4,317,851 ¥ 3,627,502
[1] Accrued interest receivables of ¥20,845 million at March 31, 2025, and ¥29,997 million at March 31, 2026 are excluded from amortized cost and included in Accrued income.
[2] Amortized cost, net of the allowance for credit losses, of which the amounts related to available-for-sale securities were ¥nil at both March 31, 2025 and 2026.
[3] Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥315,536 million and ¥22 million, respectively, at March 31, 2025, and ¥281,815 million and ¥21 million, respectively, at March 31, 2026. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association (“Ginnie Mae”) securities, which are guaranteed by the United States government.
[4] Other debt securities presented in this line primarily consist of Foreign negotiable certificates of deposit (“NCDs”) and asset-backed securities (“ABS”), of which the total fair values were ¥221,706 million at March 31, 2025, and ¥287,547 million at March 31, 2026.
[5] All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.