Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Mar. 31, 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	$ 9,037,646
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	532,200
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	416,542
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	44,190
Debt Securities, Available-for-sale, Unrealized Loss Position	9,454,188
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	576,390	$ 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	3,220,375
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	152,643
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	3,220,375
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	152,643	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	4,583,657
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	286,421
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	402,940
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	41,692
Debt Securities, Available-for-sale, Unrealized Loss Position	4,986,597
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	328,113	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	1,233,614
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	93,136
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13,602
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,498
Debt Securities, Available-for-sale, Unrealized Loss Position	1,247,216
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 95,634	$ 5,374