Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - Net interest income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives	$ 49	$ (117)
Gain (Loss) on Hedged Items	17	134
Asset-backed securities available-for-sale | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives	117	(177)
Gain (Loss) on Hedged Items	81	344
Deposits | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives	5	8
Gain (Loss) on Hedged Items	(21)	(31)
Long-term debt | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives	(73)	52
Gain (Loss) on Hedged Items	$ (43)	$ (179)