Derivatives - Derivatives Associated with Interest Rate Risk Management Activities (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 4,201	$ 4,301
Assets	13	22
Liabilities	108	104
Customer interest rate contracts | Customer Interest Rate Contracts Hedging  | Hedging Instruments and Hedged Items:
Derivative Instruments, Gain (Loss) [Line Items]
Notional	8,096	7,851
Assets	28	43
Liabilities	190	185
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	4,335	4,446
Assets	74	70
Liabilities	13	22
Offsetting upstream interest rate contracts | Customer Interest Rate Contracts Hedging  | Hedging Instruments and Hedged Items:
Derivative Instruments, Gain (Loss) [Line Items]
Notional	8,396	8,151
Assets	189	184
Liabilities	$ 28	$ 43