v3.25.2
Severance Indemnities and Pension Plans (Fair Values of Investments Valued at Net Asset per Share (or Its Equivalent) for Pension Benefits and SIP Investments) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2025
Mar. 31, 2024
Domestic, Japan | Pension benefits and SIPs    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) ¥ 1,863,599 ¥ 1,795,402
Domestic, Japan | Pension benefits and SIPs | Mutual funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 977,917 899,855
Domestic, Japan | Pension benefits and SIPs | Real estate funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 11,205 11,876
Domestic, Japan | Pension benefits and SIPs | Total pooled funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 844,187 854,076
Domestic, Japan | Pension benefits and SIPs | Total pooled funds | Japanese marketable equity securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 63,276 74,802
Domestic, Japan | Pension benefits and SIPs | Total pooled funds | Japanese debt securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 191,765 203,075
Domestic, Japan | Pension benefits and SIPs | Total pooled funds | Non-Japanese marketable equity securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 166,045 195,320
Domestic, Japan | Pension benefits and SIPs | Total pooled funds | Non-Japanese debt securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 288,808 290,985
Domestic, Japan | Pension benefits and SIPs | Total pooled funds | Other    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 134,293 89,894
Domestic, Japan | Pension benefits and SIPs | Other investment funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 1,019,412 941,326
Foreign offices and subsidiaries | Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 75,771 88,717
Foreign offices and subsidiaries | Pension benefits | Total pooled funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Total pooled funds | Japanese marketable equity securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Total pooled funds | Japanese debt securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Total pooled funds | Non-Japanese marketable equity securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Total pooled funds | Non-Japanese debt securities    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Total pooled funds | Other    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 0 0
Foreign offices and subsidiaries | Pension benefits | Other investment funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 75,771 88,717
Foreign offices and subsidiaries | Pension benefits | Other investment funds | Mutual funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 5,787 5,983
Foreign offices and subsidiaries | Pension benefits | Other investment funds | Real estate funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 39,712 50,248
Foreign offices and subsidiaries | Pension benefits | Other investment funds | Common collective funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) ¥ 30,093 ¥ 32,294