v3.26.1
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, 2026
Mar. 31, 2025
Domestic, Japan | Pension benefits and SIPs    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) ¥ 2,178,540 ¥ 1,863,599
Domestic, Japan | Pension benefits and SIPs | Mutual funds    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 1,197,658 977,917
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) 12,177 11,205
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) 936,658 844,187
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) 58,187 63,276
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) 291,581 191,765
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) 202,174 166,045
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) 238,730 288,808
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) 145,986 134,293
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) 1,241,882 1,019,412
Foreign offices and subsidiaries | Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Investments valued at net asset per share (or its equivalent) 66,432 75,771
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) 66,432 75,771
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) 6,226 5,787
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) 28,207 39,712
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) ¥ 31,840 ¥ 30,093