Fair Value (Assets and Liabilities Measured at Fair Value by Level on Recurring Basis) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2022
Mar. 31, 2021
Assets    
Trading derivative assets ¥ 10,534,000 ¥ 11,997,000
Available-for-sale debt securities, Fair value 45,798,442 47,117,813
Equity securities 5,422,200 6,222,920
Liabilities    
Trading derivative liabilities 10,895,000 11,714,000
Obligation to return securities received as collateral 6,826,215 6,581,759
Disposal group, disposed of by sale, not discontinued operations    
Assets    
Assets held for sale relating to transferred business of MUFG Union Bank (Note 2) 11,621,567 0
Liabilities held for sale:    
Other 11,157,660 0
Interest rate contracts    
Assets    
Trading derivative assets 5,445,000 7,718,000
Liabilities    
Trading derivative liabilities 5,652,000 7,361,000
Foreign exchange contracts    
Assets    
Trading derivative assets 4,803,000 3,910,000
Liabilities    
Trading derivative liabilities 4,908,000 4,027,000
Equity contracts    
Assets    
Trading derivative assets 151,000 231,000
Liabilities    
Trading derivative liabilities 277,000 237,000
Commodity contracts    
Assets    
Trading derivative assets 22,000 27,000
Liabilities    
Trading derivative liabilities 22,000 27,000
Credit derivatives    
Assets    
Trading derivative assets 103,000 94,000
Liabilities    
Trading derivative liabilities 101,000 109,000
Other    
Assets    
Trading derivative assets 10,000 17,000
Liabilities    
Trading derivative liabilities (65,000) (47,000)
Japanese national government and Japanese government agency bonds    
Assets    
Available-for-sale debt securities, Fair value 34,327,764 35,273,211
Japanese prefectural and municipal bonds    
Assets    
Available-for-sale debt securities, Fair value 4,146,144 3,731,513
Foreign government and official institution bonds    
Assets    
Available-for-sale debt securities, Fair value 2,631,343 2,926,963
Corporate bonds    
Assets    
Available-for-sale debt securities, Fair value 1,090,148 1,134,270
Residential mortgage-backed securities    
Assets    
Available-for-sale debt securities, Fair value 900,407 1,467,130
Commercial mortgage-backed securities    
Assets    
Available-for-sale debt securities, Fair value   464,565
Asset-backed securities    
Assets    
Available-for-sale debt securities, Fair value 1,588,420 1,384,485
Other debt securities    
Assets    
Available-for-sale debt securities, Fair value 103,579 171,578
Commercial paper    
Assets    
Available-for-sale debt securities, Fair value 1,010,637 564,098
Fair Value, Measurements, Recurring    
Assets    
Trading account assets: 31,967,627 32,360,686
Trading derivative assets 10,521,431 11,981,438
Available-for-sale debt securities, Fair value 45,798,442 47,117,813
Equity securities 5,042,026 5,805,061
Other 1,477,532 1,263,701
Assets held for sale:    
Total 98,098,401 98,528,699
Liabilities    
Trading securities sold, not yet purchased 59,826 261,138
Trading derivative liabilities 10,959,220 11,756,415
Obligation to return securities received as collateral 6,826,215 6,581,759
Other 541,598 556,341
Liabilities held for sale 53,199  
Liabilities held for sale:    
Other 53,199  
Total 18,440,058 19,155,653
Fair Value, Measurements, Recurring | Disposal group, disposed of by sale, not discontinued operations    
Assets    
Assets held for sale relating to transferred business of MUFG Union Bank (Note 2) 3,291,343  
Assets held for sale:    
Investment securities 3,188,257  
Other 103,086  
Fair Value, Measurements, Recurring | Equity securities    
Assets    
Trading account assets: 2,904,839 3,464,628
Fair Value, Measurements, Recurring | Equity securities | NAV of private equity funds    
Liabilities held for sale:    
Investment securities valued at net asset value 179,278 102,255
Unfunded commitments 110,360 97,413
Fair Value, Measurements, Recurring | Level 1    
Assets    
Trading account assets: 17,170,976 18,439,146
Trading derivative assets 201,860 136,515
Available-for-sale debt securities, Fair value 32,672,696 34,010,613
Equity securities 4,834,102 5,530,077
Other 1,434,046 1,202,230
Assets held for sale:    
Total 56,735,130 59,318,581
Liabilities    
Trading securities sold, not yet purchased 57,371 260,149
Trading derivative liabilities 217,570 150,750
Obligation to return securities received as collateral 6,670,482 6,484,452
Other 0 0
Liabilities held for sale:    
Other 852  
Total 6,946,275 6,895,351
Fair Value, Measurements, Recurring | Level 1 | Disposal group, disposed of by sale, not discontinued operations    
Assets    
Assets held for sale relating to transferred business of MUFG Union Bank (Note 2) 421,450  
Assets held for sale:    
Investment securities 409,618  
Other 11,832  
Liabilities    
Liabilities held for sale 852  
Fair Value, Measurements, Recurring | Level 1 | Equity securities    
Assets    
Trading account assets: 1,633,726 2,125,587
Fair Value, Measurements, Recurring | Level 2    
Assets    
Trading account assets: 13,998,654 13,165,127
Trading derivative assets 10,204,531 11,774,865
Available-for-sale debt securities, Fair value 12,912,810 12,817,584
Equity securities 152,041 229,415
Other 38,574 42,687
Assets held for sale:    
Total 40,097,982 38,029,678
Liabilities    
Trading securities sold, not yet purchased 2,455 989
Trading derivative liabilities 10,697,699 11,560,634
Obligation to return securities received as collateral 155,733 97,307
Other 525,135 558,553
Liabilities held for sale 50,744  
Liabilities held for sale:    
Other 50,744  
Total 11,431,766 12,217,483
Fair Value, Measurements, Recurring | Level 2 | Disposal group, disposed of by sale, not discontinued operations    
Assets    
Assets held for sale relating to transferred business of MUFG Union Bank (Note 2) 2,791,372  
Assets held for sale:    
Investment securities 2,713,377  
Other 77,995  
Fair Value, Measurements, Recurring | Level 2 | Equity securities    
Assets    
Trading account assets: 1,103,907 1,199,431
Fair Value, Measurements, Recurring | Level 3    
Assets    
Trading account assets: 797,997 756,413
Trading derivative assets 115,040 70,058
Available-for-sale debt securities, Fair value 212,936 289,616
Equity securities 55,883 45,569
Other 4,912 18,784
Assets held for sale:    
Total 1,265,289 1,180,440
Liabilities    
Trading securities sold, not yet purchased 0 0
Trading derivative liabilities 43,951 45,031
Obligation to return securities received as collateral 0 0
Other 16,463 (2,212)
Liabilities held for sale 1,603  
Liabilities held for sale:    
Other 1,603  
Total 62,017 42,819
Fair Value, Measurements, Recurring | Level 3 | Disposal group, disposed of by sale, not discontinued operations    
Assets    
Assets held for sale relating to transferred business of MUFG Union Bank (Note 2) 78,521  
Assets held for sale:    
Investment securities 65,262  
Other 13,259  
Fair Value, Measurements, Recurring | Level 3 | Equity securities    
Assets    
Trading account assets: 167,206 139,610
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds    
Assets    
Available-for-sale debt securities, Fair value 34,327,764 35,273,211
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Debt securities    
Assets    
Trading account assets: 8,271,741 7,201,833
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 1    
Assets    
Available-for-sale debt securities, Fair value 30,989,319 32,073,409
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 1 | Debt securities    
Assets    
Trading account assets: 7,927,707 6,800,379
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 2    
Assets    
Available-for-sale debt securities, Fair value 3,338,445 3,199,802
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 2 | Debt securities    
Assets    
Trading account assets: 344,034 401,454
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 3    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Japanese national government and Japanese government agency bonds | Level 3 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds    
Assets    
Available-for-sale debt securities, Fair value 4,146,144 3,731,513
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Debt securities    
Assets    
Trading account assets: 132,097 193,936
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 1 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 2    
Assets    
Available-for-sale debt securities, Fair value 4,146,144 3,731,513
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 2 | Debt securities    
Assets    
Trading account assets: 132,097 193,936
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 3    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Japanese prefectural and municipal bonds | Level 3 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Foreign government and official institution bonds    
Assets    
Available-for-sale debt securities, Fair value 2,631,343 2,926,963
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Debt securities    
Assets    
Trading account assets: 8,079,219 9,959,753
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 1    
Assets    
Available-for-sale debt securities, Fair value 1,683,377 1,937,204
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 1 | Debt securities    
Assets    
Trading account assets: 7,606,345 9,508,030
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 2    
Assets    
Available-for-sale debt securities, Fair value 936,076 973,041
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 2 | Debt securities    
Assets    
Trading account assets: 471,163 450,443
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 3    
Assets    
Available-for-sale debt securities, Fair value 11,890 16,718
Fair Value, Measurements, Recurring | Foreign government and official institution bonds | Level 3 | Debt securities    
Assets    
Trading account assets: 1,711 1,280
Fair Value, Measurements, Recurring | Corporate bonds    
Assets    
Available-for-sale debt securities, Fair value 1,090,148 1,134,270
Fair Value, Measurements, Recurring | Corporate bonds | Debt securities    
Assets    
Trading account assets: 2,668,750 2,711,811
Fair Value, Measurements, Recurring | Corporate bonds | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Corporate bonds | Level 1 | Debt securities    
Assets    
Trading account assets: 3,198 5,123
Fair Value, Measurements, Recurring | Corporate bonds | Level 2    
Assets    
Available-for-sale debt securities, Fair value 1,087,059 1,134,108
Fair Value, Measurements, Recurring | Corporate bonds | Level 2 | Debt securities    
Assets    
Trading account assets: 2,664,869 2,706,611
Fair Value, Measurements, Recurring | Corporate bonds | Level 3    
Assets    
Available-for-sale debt securities, Fair value 3,089 162
Fair Value, Measurements, Recurring | Corporate bonds | Level 3 | Debt securities    
Assets    
Trading account assets: 683 77
Fair Value, Measurements, Recurring | Residential mortgage-backed securities    
Assets    
Available-for-sale debt securities, Fair value 900,407 1,467,130
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Debt securities    
Assets    
Trading account assets: 6,792,386 6,167,340
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 1 | Debt securities    
Assets    
Trading account assets: 0 27
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 2    
Assets    
Available-for-sale debt securities, Fair value 900,392 1,467,115
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 2 | Debt securities    
Assets    
Trading account assets: 6,792,386 6,166,313
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 3    
Assets    
Available-for-sale debt securities, Fair value 15 15
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Level 3 | Debt securities    
Assets    
Trading account assets: 0 1,000
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities    
Assets    
Available-for-sale debt securities, Fair value   464,565
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Debt securities    
Assets    
Trading account assets: 7,402  
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 1    
Assets    
Available-for-sale debt securities, Fair value   0
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 1 | Debt securities    
Assets    
Trading account assets: 0  
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 2    
Assets    
Available-for-sale debt securities, Fair value   462,966
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 2 | Debt securities    
Assets    
Trading account assets: 7,402  
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 3    
Assets    
Available-for-sale debt securities, Fair value   1,599
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Level 3 | Debt securities    
Assets    
Trading account assets: 0  
Fair Value, Measurements, Recurring | Asset-backed securities    
Assets    
Available-for-sale debt securities, Fair value 1,588,420 1,384,485
Fair Value, Measurements, Recurring | Asset-backed securities | Debt securities    
Assets    
Trading account assets: 1,526,106 1,382,517
Fair Value, Measurements, Recurring | Asset-backed securities | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Asset-backed securities | Level 1 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Asset-backed securities | Level 2    
Assets    
Available-for-sale debt securities, Fair value 1,464,041 1,247,565
Fair Value, Measurements, Recurring | Asset-backed securities | Level 2 | Debt securities    
Assets    
Trading account assets: 1,210,875 1,045,706
Fair Value, Measurements, Recurring | Asset-backed securities | Level 3    
Assets    
Available-for-sale debt securities, Fair value 124,379 136,920
Fair Value, Measurements, Recurring | Asset-backed securities | Level 3 | Debt securities    
Assets    
Trading account assets: 315,231 336,811
Fair Value, Measurements, Recurring | Other debt securities    
Assets    
Available-for-sale debt securities, Fair value 103,579 171,578
Fair Value, Measurements, Recurring | Other debt securities | Debt securities    
Assets    
Trading account assets: 313,166 277,635
Fair Value, Measurements, Recurring | Other debt securities | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Other debt securities | Level 1 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Other debt securities | Level 2    
Assets    
Available-for-sale debt securities, Fair value 30,016 37,376
Fair Value, Measurements, Recurring | Other debt securities | Level 2 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Other debt securities | Level 3    
Assets    
Available-for-sale debt securities, Fair value 73,563 134,202
Fair Value, Measurements, Recurring | Other debt securities | Level 3 | Debt securities    
Assets    
Trading account assets: 313,166 277,635
Fair Value, Measurements, Recurring | Commercial paper    
Assets    
Available-for-sale debt securities, Fair value 1,010,637 564,098
Fair Value, Measurements, Recurring | Commercial paper | Debt securities    
Assets    
Trading account assets: 1,271,921 1,001,233
Fair Value, Measurements, Recurring | Commercial paper | Level 1    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Commercial paper | Level 1 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Commercial paper | Level 2    
Assets    
Available-for-sale debt securities, Fair value 1,010,637 564,098
Fair Value, Measurements, Recurring | Commercial paper | Level 2 | Debt securities    
Assets    
Trading account assets: 1,271,921 1,001,233
Fair Value, Measurements, Recurring | Commercial paper | Level 3    
Assets    
Available-for-sale debt securities, Fair value 0 0
Fair Value, Measurements, Recurring | Commercial paper | Level 3 | Debt securities    
Assets    
Trading account assets: 0 0
Fair Value, Measurements, Recurring | Marketable equity securities    
Assets    
Equity securities 4,986,143 5,759,492
Fair Value, Measurements, Recurring | Marketable equity securities | Level 1    
Assets    
Equity securities 4,834,102 5,530,077
Fair Value, Measurements, Recurring | Marketable equity securities | Level 2    
Assets    
Equity securities 152,041 229,415
Fair Value, Measurements, Recurring | Marketable equity securities | Level 3    
Assets    
Equity securities 0 0
Fair Value, Measurements, Recurring | Nonmarketable equity securities    
Assets    
Equity securities 55,883 45,569
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Private equity funds    
Liabilities held for sale:    
Unfunded commitments 0 4,758
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Real estate funds    
Liabilities held for sale:    
Investment securities valued at net asset value 30,142 27,395
Unfunded commitments 1,011 1,006
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Private equity and other funds    
Liabilities held for sale:    
Investment securities valued at net asset value 39,462 34,390
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Level 1    
Assets    
Equity securities 0 0
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Level 2    
Assets    
Equity securities 0 0
Fair Value, Measurements, Recurring | Nonmarketable equity securities | Level 3    
Assets    
Equity securities 55,883 45,569
Fair Value, Measurements, Recurring | Interest rate contracts    
Assets    
Trading derivative assets 5,444,683 7,717,955
Liabilities    
Trading derivative liabilities 5,651,690 7,361,129
Fair Value, Measurements, Recurring | Interest rate contracts | Level 1    
Assets    
Trading derivative assets 121,584 23,906
Liabilities    
Trading derivative liabilities 19,841 10,696
Fair Value, Measurements, Recurring | Interest rate contracts | Level 2    
Assets    
Trading derivative assets 5,268,790 7,673,031
Liabilities    
Trading derivative liabilities 5,615,033 7,343,594
Fair Value, Measurements, Recurring | Interest rate contracts | Level 3    
Assets    
Trading derivative assets 54,309 21,018
Liabilities    
Trading derivative liabilities 16,816 6,839
Fair Value, Measurements, Recurring | Foreign exchange contracts    
Assets    
Trading derivative assets 4,800,813 3,910,162
Liabilities    
Trading derivative liabilities 4,907,168 4,022,141
Fair Value, Measurements, Recurring | Foreign exchange contracts | Level 1    
Assets    
Trading derivative assets 2,514 929
Liabilities    
Trading derivative liabilities 4,017 977
Fair Value, Measurements, Recurring | Foreign exchange contracts | Level 2    
Assets    
Trading derivative assets 4,788,739 3,896,713
Liabilities    
Trading derivative liabilities 4,901,054 4,015,927
Fair Value, Measurements, Recurring | Foreign exchange contracts | Level 3    
Assets    
Trading derivative assets 9,560 12,520
Liabilities    
Trading derivative liabilities 2,097 5,237
Fair Value, Measurements, Recurring | Equity contracts    
Assets    
Trading derivative assets 150,948 231,575
Liabilities    
Trading derivative liabilities 277,077 237,418
Fair Value, Measurements, Recurring | Equity contracts | Level 1    
Assets    
Trading derivative assets 77,762 111,680
Liabilities    
Trading derivative liabilities 193,712 139,077
Fair Value, Measurements, Recurring | Equity contracts | Level 2    
Assets    
Trading derivative assets 47,207 113,586
Liabilities    
Trading derivative liabilities 80,806 92,655
Fair Value, Measurements, Recurring | Equity contracts | Level 3    
Assets    
Trading derivative assets 25,979 6,309
Liabilities    
Trading derivative liabilities 2,559 5,686
Fair Value, Measurements, Recurring | Commodity contracts    
Assets    
Trading derivative assets 22,072 26,897
Liabilities    
Trading derivative liabilities 22,029 26,960
Fair Value, Measurements, Recurring | Commodity contracts | Level 1    
Assets    
Trading derivative assets 0 0
Liabilities    
Trading derivative liabilities 0 0
Fair Value, Measurements, Recurring | Commodity contracts | Level 2    
Assets    
Trading derivative assets 88 1
Liabilities    
Trading derivative liabilities 0 1
Fair Value, Measurements, Recurring | Commodity contracts | Level 3    
Assets    
Trading derivative assets 21,984 26,896
Liabilities    
Trading derivative liabilities 22,029 26,959
Fair Value, Measurements, Recurring | Credit derivatives    
Assets    
Trading derivative assets 102,515 93,888
Liabilities    
Trading derivative liabilities 100,885 108,540
Fair Value, Measurements, Recurring | Credit derivatives | Level 1    
Assets    
Trading derivative assets 0 0
Liabilities    
Trading derivative liabilities 0 0
Fair Value, Measurements, Recurring | Credit derivatives | Level 2    
Assets    
Trading derivative assets 99,707 91,534
Liabilities    
Trading derivative liabilities 100,806 108,457
Fair Value, Measurements, Recurring | Credit derivatives | Level 3    
Assets    
Trading derivative assets 2,808 2,354
Liabilities    
Trading derivative liabilities 79 83
Fair Value, Measurements, Recurring | Other    
Assets    
Trading derivative assets 400 961
Liabilities    
Trading derivative liabilities 371 227
Fair Value, Measurements, Recurring | Other | Level 1    
Assets    
Trading derivative assets 0 0
Liabilities    
Trading derivative liabilities 0 0
Fair Value, Measurements, Recurring | Other | Level 2    
Assets    
Trading derivative assets 0 0
Liabilities    
Trading derivative liabilities 0 0
Fair Value, Measurements, Recurring | Other | Level 3    
Assets    
Trading derivative assets 400 961
Liabilities    
Trading derivative liabilities ¥ 371 ¥ 227