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Retirement and Benefit Plans - Assumptions used in Calculating Benefit Obligation (Details) - Pension Plan - Acquired Comerica Plans
5 Months Ended
Jun. 30, 2026
Qualified Plan  
Defined Benefit Plan Disclosure [Line Items]  
Discount rate 5.79%
Rate of compensation increase 4.50%
Expected long-term return on plan assets 6.75%
Qualified Plan | Minimum  
Defined Benefit Plan Disclosure [Line Items]  
Interest crediting rate 4.87%
Qualified Plan | Maximum  
Defined Benefit Plan Disclosure [Line Items]  
Interest crediting rate 5.25%
Nonqualified Plan  
Defined Benefit Plan Disclosure [Line Items]  
Discount rate 5.75%
Rate of compensation increase 4.50%
Nonqualified Plan | Minimum  
Defined Benefit Plan Disclosure [Line Items]  
Interest crediting rate 4.87%
Nonqualified Plan | Maximum  
Defined Benefit Plan Disclosure [Line Items]  
Interest crediting rate 5.25%