Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 5,952,140
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	104,150
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	8,880,745
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,326,577
Debt Securities, Available-for-sale, Unrealized Loss Position	14,832,885
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,430,727	$ 1,681,985
U.S. Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,033,194
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	44,859
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3,094,902
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	280,630
Debt Securities, Available-for-sale, Unrealized Loss Position	5,128,096
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	325,489	398,959
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,665,095
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	36,196
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,330,689
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	812,153
Debt Securities, Available-for-sale, Unrealized Loss Position	5,995,784
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	848,349	948,638
States and political subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,253,851
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	23,095
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,455,154
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	233,794
Debt Securities, Available-for-sale, Unrealized Loss Position	3,709,005
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 256,889	$ 334,388