Fees and Commissions Income (Details of Fees and Commissions Income) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Mar. 31, 2020
Disaggregation of Contract Revenue [Line Items]      
Total ¥ 1,658,863 ¥ 1,527,283 ¥ 1,502,052
Fees and commissions on deposits      
Disaggregation of Contract Revenue [Line Items]      
Total 51,032 50,131 53,684
Fees and commissions on remittances and transfers      
Disaggregation of Contract Revenue [Line Items]      
Total 157,236 165,288 169,407
Fees and commissions on foreign trading business      
Disaggregation of Contract Revenue [Line Items]      
Total 56,344 79,353 66,025
Fees and commissions on credit card business      
Disaggregation of Contract Revenue [Line Items]      
Total 207,080 199,625 238,112
Fees and commissions on security-related services      
Disaggregation of Contract Revenue [Line Items]      
Total 264,530 244,017 221,494
Fees and commissions on administration and management services for investment funds      
Disaggregation of Contract Revenue [Line Items]      
Total 286,549 235,497 184,559
Trust fees      
Disaggregation of Contract Revenue [Line Items]      
Total 133,322 125,658 119,919
Guarantee fees      
Disaggregation of Contract Revenue [Line Items]      
Total 45,849 43,889 46,322
Insurance commissions      
Disaggregation of Contract Revenue [Line Items]      
Total 42,353 42,117 44,415
Fees and commissions on real estate business      
Disaggregation of Contract Revenue [Line Items]      
Total 65,611 48,110 49,764
Other fees and commissions      
Disaggregation of Contract Revenue [Line Items]      
Total ¥ 348,957 ¥ 293,598 ¥ 308,351