Loans and Allowance for Credit Losses (Changes in Allowance for Credit Losses by Portfolio Segment) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year ¥ 1,348,391 [1] ¥ 809,540 ¥ 658,184
Provision for (reversal of) credit losses 277,995 484,210 321,713
Charge-offs 238,012 290,506 243,135
Recoveries collected 58,715 45,082 63,858
Net charge-offs 179,297 245,424 179,277
Other 23,612 (23,639) 8,920
Balance at end of fiscal year 1,470,701 [1] 1,348,391 [1] 809,540
Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 323,704    
Balance at end of fiscal year   323,704  
Commercial      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 734,577 482,275 389,615
Provision for (reversal of) credit losses 236,659 235,584 153,782
Charge-offs 57,848 77,904 85,326
Recoveries collected 11,898 9,262 26,427
Net charge-offs 45,950 68,642 58,899
Other 8,800 1,532 (2,223)
Balance at end of fiscal year 934,086 734,577 482,275
Commercial | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 83,828    
Balance at end of fiscal year   83,828  
Residential      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 82,893 34,746 38,626
Provision for (reversal of) credit losses (10,899) 1,385 (1,028)
Charge-offs 2,121 2,745 3,227
Recoveries collected 14 13 375
Net charge-offs 2,107 2,732 2,852
Other 0 0 0
Balance at end of fiscal year 69,887 82,893 34,746
Residential | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 49,494    
Balance at end of fiscal year   49,494  
Card      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 44,217 35,180 32,550
Provision for (reversal of) credit losses 15,473 17,876 26,542
Charge-offs 20,153 24,564 25,149
Recoveries collected 1,231 1,463 1,237
Net charge-offs 18,922 23,101 23,912
Other 0 0 0
Balance at end of fiscal year 40,768 44,217 35,180
Card | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 14,262    
Balance at end of fiscal year   14,262  
MUAH      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 131,755 58,995 52,581
Provision for (reversal of) credit losses (101,112) 90,064 30,825
Charge-offs 19,208 40,376 27,934
Recoveries collected 9,532 4,362 4,173
Net charge-offs 9,676 36,014 23,761
Other 9,398 (6,327) (650)
Balance at end of fiscal year 30,365 131,755 58,995
MUAH | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 25,037    
Balance at end of fiscal year   25,037  
Krungsri      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 293,396 169,626 144,812
Provision for (reversal of) credit losses 90,514 90,167 70,023
Charge-offs 83,474 93,192 77,907
Recoveries collected 22,890 23,415 23,170
Net charge-offs 60,584 69,777 54,737
Other (940) (14,953) 9,528
Balance at end of fiscal year 322,386 293,396 169,626
Krungsri | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 118,333    
Balance at end of fiscal year   118,333  
Other      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year 61,553 28,718 0
Provision for (reversal of) credit losses 47,360 49,134 41,569
Charge-offs 55,208 51,725 23,592
Recoveries collected 13,150 6,567 8,476
Net charge-offs 42,058 45,158 15,116
Other 6,354 (3,891) 2,265
Balance at end of fiscal year 73,209 61,553 ¥ 28,718
Other | Cumulative effect adjustment | Effect of adopting new guidance on measurement of credit losses on financial instruments      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Balance at beginning of fiscal year ¥ 32,750    
Balance at end of fiscal year   ¥ 32,750  
[1] New guidance on measurement of credit losses on financial instruments requires the allowance for credit losses to be measured using the current expected credit losses model from April 1, 2020. For additional information, refer to Note 1.