Severance Indemnities and Pension Plans (Combined Funded Status and Amounts Recognized in Consolidated Balance Sheets) (Detail) - JPY (¥)
12 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Mar. 31, 2020
Amounts recognized in the consolidated balance sheets:      
Prepaid benefit cost ¥ 1,356,603,000,000 ¥ 1,223,706,000,000  
Accrued benefit cost (89,062,000,000) (93,730,000,000)  
Domestic, Japan | Non-contributory pension benefits and SIP      
Change in benefit obligation:      
Benefit obligation at beginning of fiscal year 1,753,483,000,000 1,807,905,000,000  
Service cost 44,160,000,000 46,861,000,000  
Interest cost 11,995,000,000 11,091,000,000  
Plan participants’ contributions 0 0  
Acquisitions/ Divestitures 242,000,000 2,845,000,000  
Amendments (1,054,000,000) (22,000,000)  
Actuarial loss (gain) (28,814,000,000) (21,558,000,000)  
Benefits paid (65,853,000,000) (65,730,000,000)  
Lump-sum payment (21,570,000,000) (22,219,000,000)  
Translation adjustments and other 0 0  
Benefit obligation at end of fiscal year 1,692,105,000,000 1,753,483,000,000 ¥ 1,807,905,000,000
Change in plan assets:      
Fair value of plan assets at beginning of fiscal year 2,858,013,000,000 2,432,847,000,000  
Actual return on plan assets 77,848,000,000 472,185,000,000  
Employer contributions 20,487,000,000 21,151,000,000  
Acquisitions/ Divestitures 8,000,000 (2,440,000,000)  
Plan participants’ contributions 0 0  
Benefits paid (65,853,000,000) (65,730,000,000)  
Translation adjustments and other 0 0  
Fair value of plan assets at end of fiscal year 2,890,503,000,000 2,858,013,000,000 2,432,847,000,000
Amounts recognized in the consolidated balance sheets:      
Prepaid benefit cost 1,216,703,000,000 1,122,507,000,000  
Accrued benefit cost (18,305,000,000) (17,977,000,000)  
Net amount recognized 1,198,398,000,000 1,104,530,000,000  
Foreign offices and subsidiaries | Pension benefits      
Change in benefit obligation:      
Benefit obligation at beginning of fiscal year 580,953,000,000 547,013,000,000  
Service cost 16,853,000,000 13,947,000,000 14,406,000,000
Interest cost 11,233,000,000 14,295,000,000 17,370,000,000
Plan participants’ contributions 0 30,000,000  
Acquisitions/ Divestitures 130,000,000 260,000,000  
Amendments 402,000,000 (1,187,000,000)  
Actuarial loss (gain) (24,611,000,000) 51,724,000,000  
Benefits paid (24,501,000,000) (20,816,000,000)  
Lump-sum payment (3,591,000,000) (2,825,000,000)  
Translation adjustments and other (63,131,000,000) 20,968,000,000  
Benefit obligation at end of fiscal year 619,739,000,000 580,953,000,000 547,013,000,000
Change in plan assets:      
Fair value of plan assets at beginning of fiscal year 604,404,000,000 559,508,000,000  
Actual return on plan assets 49,277,000,000 82,615,000,000  
Employer contributions 4,627,000,000 3,896,000,000  
Acquisitions/ Divestitures 0 0  
Plan participants’ contributions 0 30,000,000  
Benefits paid (24,501,000,000) (20,816,000,000)  
Translation adjustments and other 72,057,000,000 (20,829,000,000)  
Fair value of plan assets at end of fiscal year 705,864,000,000 604,404,000,000 559,508,000,000
Amounts recognized in the consolidated balance sheets:      
Prepaid benefit cost 153,861,000,000 94,445,000,000  
Accrued benefit cost (67,736,000,000) (70,994,000,000)  
Net amount recognized 86,125,000,000 23,451,000,000  
Foreign offices and subsidiaries | Other benefits      
Change in benefit obligation:      
Benefit obligation at beginning of fiscal year 31,354,000,000 32,383,000,000  
Service cost 140,000,000 229,000,000 366,000,000
Interest cost 494,000,000 793,000,000 1,159,000,000
Plan participants’ contributions 433,000,000 440,000,000  
Acquisitions/ Divestitures 0 0  
Amendments 0 0  
Actuarial loss (gain) (2,269,000,000) 1,506,000,000  
Benefits paid (2,580,000,000) (2,488,000,000)  
Lump-sum payment 0 0  
Translation adjustments and other (3,219,000,000) 1,509,000,000  
Benefit obligation at end of fiscal year 30,791,000,000 31,354,000,000 32,383,000,000
Change in plan assets:      
Fair value of plan assets at beginning of fiscal year 33,349,000,000 31,919,000,000  
Actual return on plan assets 4,619,000,000 5,165,000,000  
Employer contributions   181,000,000  
Acquisitions/ Divestitures 0 0  
Plan participants’ contributions 433,000,000 440,000,000  
Benefits paid (2,580,000,000) (2,488,000,000)  
Translation adjustments and other 3,823,000,000 (1,868,000,000)  
Fair value of plan assets at end of fiscal year 39,528,000,000 33,349,000,000 ¥ 31,919,000,000
Amounts recognized in the consolidated balance sheets:      
Prepaid benefit cost 12,104,000,000 6,754,000,000  
Accrued benefit cost (3,367,000,000) (4,759,000,000)  
Net amount recognized 8,737,000,000 ¥ 1,995,000,000  
Foreign offices and subsidiaries | Other benefits netting      
Change in plan assets:      
Employer contributions ¥ (116,000,000)