Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt securities available for sale:
Due in one year or less	$ 3,248
Due after one year through five years	4,691
Due after five years through ten years	50
Total available for sale (amortized cost)	7,989
Mortgage-backed securities	4,408
Investment securities available for sale, amortized cost	12,397	$ 10,691
Debt securities held to maturity:
Due in one year or less	588
Due after one year through five years	635
Due after five years through ten years	1,369
Due after ten years	883
Total available for held to maturity (amortized cost)	3,475
Mortgage-backed securities	11,603
Amortized cost for held to maturity	15,078	15,330
Debt securities available for sale:
Due in one year or less	3,209
Due after one year through five years	4,628
Due after five years through ten years	44
Total available for sale (fair value)	7,881
Mortgage-backed securities	4,253
Total	12,134	10,440
Debt securities held to maturity:
Due in one year or less	575
Due after one year through five years	611
Due after five years through ten years	1,333
Due after ten years	829
Total available for held to maturity (fair value)	3,348
Mortgage-backed securities	10,517
Total	$ 13,865	$ 14,308