Loans and Allowance for Credit Losses (Total Outstanding Loans and Past Due Analysis) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2022
Mar. 31, 2021
Mar. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]      
Total ¥ 113,471,623 ¥ 116,027,745  
Loans Held for Sale 514,109 353,095  
Past Due 90 Days and Accruing 6,620 20,540  
Unearned income, unamortized premiums—net and deferred loan fees—net (322,230) (308,882)  
Total 113,149,393 115,718,863  
1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 210,279 249,200  
Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 207,798 281,701  
Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 418,077 530,901  
Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 112,539,437 115,143,749  
Residential      
Loans and Leases Receivable Disclosure [Line Items]      
Total 13,301,505 13,182,815  
Loans Held for Sale 0 0  
Past Due 90 Days and Accruing 3,360 11,150  
Residential | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 32,078 39,577  
Residential | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 13,598 28,375  
Residential | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 45,676 67,952  
Residential | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 13,255,829 13,114,863  
Card      
Loans and Leases Receivable Disclosure [Line Items]      
Total 464,266 502,241  
Loans Held for Sale 0 22,945  
Past Due 90 Days and Accruing 0 0  
Card | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 10,250 2,127  
Card | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 26,818 26,786  
Card | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 37,068 28,913  
Card | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 427,198 450,383  
MUAH      
Loans and Leases Receivable Disclosure [Line Items]      
Total 2,812,969 8,583,566  
Loans Held for Sale 70,841 87,822  
Past Due 90 Days and Accruing 0 4,626  
MUAH | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 625 42,082  
MUAH | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 0 29,337  
MUAH | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 625 71,419  
MUAH | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 2,741,503 8,424,325  
Krungsri      
Loans and Leases Receivable Disclosure [Line Items]      
Total 6,822,765 6,604,645  
Loans Held for Sale 0 0  
Past Due 90 Days and Accruing 0 0  
Krungsri | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 115,636 131,573  
Krungsri | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 126,494 127,533  
Krungsri | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 242,130 259,106  
Krungsri | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 6,580,635 6,345,539  
Other      
Loans and Leases Receivable Disclosure [Line Items]      
Total 1,045,121 986,688  
Loans Held for Sale 0 0  
Past Due 90 Days and Accruing 0 0  
Other | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 21,729 21,776  
Other | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 21,152 24,201  
Other | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 42,881 45,977  
Other | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 1,002,240 940,711  
Domestic | Commercial      
Loans and Leases Receivable Disclosure [Line Items]      
Total 54,044,718 54,680,843  
Loans Held for Sale 69,257 47,632  
Past Due 90 Days and Accruing 3,260 4,673  
Domestic | Commercial | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 12,556 4,763  
Domestic | Commercial | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 9,138 22,996  
Domestic | Commercial | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 21,694 27,759  
Domestic | Commercial | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total 53,953,767 54,605,452  
Foreign      
Loans and Leases Receivable Disclosure [Line Items]      
Total   45,338,581 ¥ 47,333,878
Foreign | Commercial      
Loans and Leases Receivable Disclosure [Line Items]      
Total 34,980,279 31,486,947  
Loans Held for Sale 374,011 194,696  
Past Due 90 Days and Accruing 0 91  
Foreign | Commercial | 1 to 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 17,405 7,302  
Foreign | Commercial | Greater than 3 months past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 10,598 22,473  
Foreign | Commercial | Total past due      
Loans and Leases Receivable Disclosure [Line Items]      
Total 28,003 29,775  
Foreign | Commercial | Financial Asset, Current      
Loans and Leases Receivable Disclosure [Line Items]      
Total ¥ 34,578,265 ¥ 31,262,476