Derivatives - Derivatives Associated with Cash Flow Hedges and Mortgage Banking Hedges (Details) - Hedging Instruments and Hedged Items:  - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Interest Rate Contract | Cash Flow Hedge
Derivative Instruments, Gain (Loss) [Line Items]
Variability in cash flows related to debt instruments (primarily loans)	$ 5,000	$ 5,000
Interest rate contracts | Cash Flow Hedge
Derivative Instruments, Gain (Loss) [Line Items]
Notional	5,000	5,000
Assets	5	0
Liabilities	38	14
Option contracts written | Mortgage Banking Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional	128	82
Assets	1	1
Liabilities	0	0
Forward contracts written | Mortgage Banking Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional	262	135
Assets	3	0
Liabilities	$ 0	$ 0