Fair Value Measurements - Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis) (Details) - Nonrecurring - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	$ 388	$ 344
OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	18	3
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	15	19
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	2	1
Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	0	10
Commercial | Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	1	40
Commercial | Commercial loans and leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	163	162
Consumer | Consumer and residential mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	189	109
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	388	335
Level 3     | OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	18	3
Level 3     | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	15	19
Level 3     | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	2	1
Level 3     | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	0	1
Level 3     | Commercial | Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	1	40
Level 3     | Commercial | Commercial loans and leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	163	162
Level 3     | Consumer | Consumer and residential mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	189	109
Level 3     | Comparable company analysis | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	0	1
Level 3     | Comparable company analysis | Commercial | Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	1	40
Level 3     | Appraised value | OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	18	3
Level 3     | Appraised value | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	15	19
Level 3     | Appraised value | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	2	1
Level 3     | Appraised value | Commercial | Commercial loans and leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	163	162
Level 3     | Appraised value | Consumer | Consumer and residential mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets, fair value	$ 189	$ 109