Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt securities available for sale:
Due in one year or less	$ 3,155,000
Due after one year through five years	4,914,000
Due after five years through ten years	0
Due after ten years	0
Total available for sale (amortized cost)	8,069,000
Mortgage-backed securities	12,738,000
Investment securities available for sale, amortized cost	20,807,000	$ 19,054,000
Debt securities held to maturity:
Due in one year or less	76,000
Due after one year through five years	614,000
Due after five years through ten years	1,459,000
Due after ten years	585,000
Total available for held to maturity (amortized cost)	2,734,000
Mortgage-backed securities	10,618,000
Amortized cost for held to maturity	13,352,000	14,195,000
Debt securities available for sale:
Due in one year or less	3,154,000
Due after one year through five years	4,935,000
Due after five years through ten years	0
Due after ten years	0
Total available for sale (fair value)	8,089,000
Mortgage-backed securities	12,710,000
Investment securities available for sale, estimated fair value	20,799,000	18,849,000
Debt securities held to maturity:
Due in one year or less	76,000
Due after one year through five years	601,000
Due after five years through ten years	1,396,000
Due after ten years	523,000
Total available for held to maturity (fair value)	2,596,000
Mortgage-backed securities	9,712,000
Estimated fair value for held to maturity	$ 12,308,000	$ 12,955,000