Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 14,653,234
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,449,969
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,819,775
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	450,621
Debt Securities, Available-for-sale, Unrealized Loss Position	16,473,009
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,900,590	$ 40,065
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	4,429,609
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	323,346
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	593,008
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	101,515
Debt Securities, Available-for-sale, Unrealized Loss Position	5,022,617
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	424,861	9,602
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	4,280,074
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	713,685
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,032,311
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	274,217
Debt Securities, Available-for-sale, Unrealized Loss Position	5,312,385
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	987,902	25,089
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	5,943,551
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	412,938
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	194,456
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	74,889
Debt Securities, Available-for-sale, Unrealized Loss Position	6,138,007
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 487,827	$ 5,374