v3.26.1
Acquisition Activity (Fair Value and Unpaid Principal Balance of Loans Acquired) (Details) - USD ($)
$ in Millions
 3 Months Ended
Jan. 05, 2026
Mar. 31, 2026
Mar. 31, 2025
Business Combination [Line Items]      
Acquired gross charge-offs   $ 45 $ 0
Total commercial lending      
Business Combination [Line Items]      
Acquired gross charge-offs   10 0
Total consumer lending      
Business Combination [Line Items]      
Acquired gross charge-offs   35 $ 0
FirstBank Holding Company      
Business Combination [Line Items]      
Net loans $ 15,177    
Acquired gross charge-offs   $ 45  
FirstBank Holding Company | Carrying Amount      
Business Combination [Line Items]      
Net loans 16,170    
Acquired gross charge-offs 45    
FirstBank Holding Company | Fair Value      
Business Combination [Line Items]      
Net loans 15,177    
FirstBank Holding Company | Total commercial lending | Carrying Amount      
Business Combination [Line Items]      
Net loans 8,517    
FirstBank Holding Company | Total commercial lending | Fair Value      
Business Combination [Line Items]      
Net loans 8,000    
FirstBank Holding Company | Total commercial lending | Commercial and industrial | Carrying Amount      
Business Combination [Line Items]      
Net loans 3,354    
FirstBank Holding Company | Total commercial lending | Commercial and industrial | Fair Value      
Business Combination [Line Items]      
Net loans 3,165    
FirstBank Holding Company | Total commercial lending | Commercial real estate | Carrying Amount      
Business Combination [Line Items]      
Net loans 5,163    
FirstBank Holding Company | Total commercial lending | Commercial real estate | Fair Value      
Business Combination [Line Items]      
Net loans 4,835    
FirstBank Holding Company | Total consumer lending | Carrying Amount      
Business Combination [Line Items]      
Net loans 7,653    
FirstBank Holding Company | Total consumer lending | Fair Value      
Business Combination [Line Items]      
Net loans 7,177    
FirstBank Holding Company | Total consumer lending | Residential real estate | Carrying Amount      
Business Combination [Line Items]      
Net loans 7,061    
FirstBank Holding Company | Total consumer lending | Residential real estate | Fair Value      
Business Combination [Line Items]      
Net loans 6,615    
FirstBank Holding Company | Total consumer lending | Home equity | Carrying Amount      
Business Combination [Line Items]      
Net loans 499    
FirstBank Holding Company | Total consumer lending | Home equity | Fair Value      
Business Combination [Line Items]      
Net loans 477    
FirstBank Holding Company | Total consumer lending | Credit card and other consumer | Carrying Amount      
Business Combination [Line Items]      
Net loans 93    
FirstBank Holding Company | Total consumer lending | Credit card and other consumer | Fair Value      
Business Combination [Line Items]      
Net loans $ 85