Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Jun. 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	$ 12,299,514
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,052,979
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	382,922
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	71,600
Debt Securities, Available-for-sale, Unrealized Loss Position	12,682,436
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,124,579	$ 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	4,224,018
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	242,690
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	4,224,018
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	242,690	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	4,825,871
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	568,405
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	369,098
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	67,116
Debt Securities, Available-for-sale, Unrealized Loss Position	5,194,969
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	635,521	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	3,249,625
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	241,884
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13,824
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,484
Debt Securities, Available-for-sale, Unrealized Loss Position	3,263,449
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 246,368	$ 5,374