v3.26.1
Accumulated other comprehensive income (loss), net of tax (Changes in Each Component of AOCI) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year ¥ 10,549,924 ¥ 10,431,187  
Less: reclassification adjustments for losses (gains) included in net income 20,217    
Change during year 405,882 (51,591) ¥ 336,163
Balance at end of fiscal year 11,478,053 10,549,924 10,431,187
Accumulated Other Comprehensive Income      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year [1] 931,779 984,578 649,395
Change during year [1] 406,133 (52,799) 335,184
Balance at end of fiscal year [1] 1,337,912 931,779 984,578
Net unrealized gains (losses) on available-for-sale securities      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year (36,056) 2,061 (31,084)
Unrealized gains (losses) during year (101,373) (48,349) 20,972
Less: reclassification adjustments for losses (gains) included in net income 54,563 10,231 12,173
Change during year (46,810) (38,118) 33,145
Balance at end of fiscal year (82,866) (36,056) 2,061
Foreign currency translation adjustments      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year 517,081 467,864 227,660
Foreign currency translation adjustments during year 312,124 52,255 258,887
Less: reclassification adjustments for losses (gains) included in net income (6,566) (3,038) (18,682)
Change during year 305,558 49,217 240,204
Balance at end of fiscal year 822,639 517,081 467,864
Defined benefit plan adjustments      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year 422,515 499,663 423,677
Unrealized gains (losses) during year 181,244 (42,062) 97,847
Less: reclassification adjustments for losses (gains) included in net income (27,714) (35,086) (21,861)
Change during year 153,530 (77,148) 75,986
Balance at end of fiscal year 576,045 422,515 499,663
Accumulated Own Credit Risk Adjustment Including Portion Attributable to Noncontrolling Interest      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Balance at beginning of fiscal year 28,239 14,990 29,142
Unrealized gains (losses) during year (6,076) 12,850 (15,403)
Less: reclassification adjustments for losses (gains) included in net income (69) 399 1,251
Change during year (6,145) 13,249 (14,152)
Balance at end of fiscal year ¥ 22,095 ¥ 28,239 ¥ 14,990
[1] The amounts that have been reclassified out of Accumulated other comprehensive income (loss), net of tax into net income are presented in Note 16 “Accumulated other comprehensive income (loss), net of tax.”