v3.26.1
Accumulated Other Comprehensive Income (Reclassification of Significant Items out of Accumulated OCI) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Investment securities gains (losses)—net ¥ (666,069) ¥ 832,533 ¥ (1,382,458)
Total before tax (2,509,495) (1,795,576) (1,878,226)
Income tax expense 625,591 527,938 500,657
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest (1,883,904) (1,267,638) (1,377,569)
Equity in earnings of equity method investees—net or Other non-interest income (871,185) (669,400) (464,054)
Other non-interest expenses (752,092) (533,961) (416,538)
Other non-interest income (550,799) (320,060) (163,603)
Amount reclassified out of Accumulated OCI      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Total before tax 220,772 115,590 114,046
Income tax expense (70,386) (35,580) (34,835)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 150,386 80,010 79,211
Amount reclassified out of Accumulated OCI | Net losses on sales and redemptions of Available-for-sale debt securities      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Investment securities gains (losses)—net 308,743 150,567 149,292
Amount reclassified out of Accumulated OCI | Impairment losses on investment securities      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Investment securities gains (losses)—net 0 12,819 2
Amount reclassified out of Accumulated OCI | Net unrealized losses on investment securities      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Investment securities gains (losses)—net 932 3,596 1,352
Total before tax 309,675 166,982 150,646
Income tax expense (98,333) (51,853) (45,320)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 211,342 115,129 105,326
Amount reclassified out of Accumulated OCI | Net debt valuation adjustments      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Total before tax 1,203 1,538 776
Income tax expense (379) (471) (237)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 824 1,067 539
Equity in earnings of equity method investees—net or Other non-interest income 1,203 1,538 776
Amount reclassified out of Accumulated OCI | Net unrealized gains (losses) on derivatives qualifying for cash flow hedges:      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Total before tax 816 3,585 (8,197)
Income tax expense (163) (717) 1,635
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 653 2,868 (6,562)
Amount reclassified out of Accumulated OCI | Net unrealized gains (losses) on derivatives qualifying for cash flow hedges: | Foreign exchange contracts      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Interest expense on Long-term debt or Foreign exchange gains (losses)—net 816 3,585 (8,197)
Amount reclassified out of Accumulated OCI | Net actuarial loss (gain)      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Other non-interest expenses (28,639) (14,798) 1,962
Amount reclassified out of Accumulated OCI | Prior service cost      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Other non-interest expenses (717) (2,059) (3,345)
Amount reclassified out of Accumulated OCI | Gain on settlements and curtailment, and other      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Other non-interest expenses (12,232) (13,178) (11,664)
Amount reclassified out of Accumulated OCI | Defined benefit plans      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Total before tax (41,587) (30,034) (13,047)
Income tax expense 13,498 9,261 4,148
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest (28,089) (20,773) (8,899)
Amount reclassified out of Accumulated OCI | Foreign currency translation adjustments      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Total before tax (49,335) (26,481) (16,132)
Income tax expense 14,991 8,200 4,939
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest (34,344) (18,281) (11,193)
Other non-interest income ¥ (49,335) ¥ (26,481) ¥ (16,132)