Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt securities available for sale:
Due in one year or less	$ 2,940
Due after one year through five years	5,007
Due after five years through ten years	0
Due after ten years	0
Total available for sale (amortized cost)	7,947
Mortgage-backed securities available for sale	11,107
Investment securities available for sale, amortized cost	19,054	$ 10,691
Debt securities held to maturity:
Due in one year or less	602
Due after one year through five years	635
Due after five years through ten years	1,491
Due after ten years	623
Total available for held to maturity (amortized cost)	3,351
Mortgage-backed securities held to maturity	10,844
Amortized cost for held to maturity	14,195	15,330
Debt securities available for sale:
Due in one year or less	2,929
Due after one year through five years	5,004
Due after five years through ten years	0
Due after ten years	0
Total available for sale (fair value)	7,933
Mortgage-backed securities available for sale	10,916
Total	18,849	10,440
Debt securities held to maturity:
Due in one year or less	602
Due after one year through five years	618
Due after five years through ten years	1,432
Due after ten years	568
Total available for held to maturity (fair value)	3,220
Mortgage-backed securities held to maturity	9,735
Total	$ 12,955	$ 14,308