v3.26.1
Fair Value Measurements - Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis) (Details) - Nonrecurring - USD ($)
$ in Millions
Mar. 31, 2026
Mar. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value $ 301 $ 423
Commercial loans and leases | Commercial    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 109 261
Consumer and residential mortgage loans | Consumer    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 166 145
OREO    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value   4
Bank premises and equipment    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 26  
Private equity investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value   13
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 301 410
Level 3 | Commercial loans and leases | Commercial    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 109 261
Level 3 | Consumer and residential mortgage loans | Consumer    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 166 145
Level 3 | OREO    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value   4
Level 3 | Bank premises and equipment    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 26  
Level 3 | Private equity investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value   0
Level 3 | Appraised Value | Commercial loans and leases | Commercial    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 109 261
Level 3 | Appraised Value | Consumer and residential mortgage loans | Consumer    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value 166 145
Level 3 | Appraised Value | OREO    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value   $ 4
Level 3 | Appraised Value | Bank premises and equipment    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Assets, fair value $ 26