Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Jun. 30, 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	$ 7,055,474
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	169,523
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9,368,445
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,448,155
Debt Securities, Available-for-sale, Unrealized Loss Position	16,423,919
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,617,678	$ 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	1,487,790
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	58,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3,585,097
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	325,531
Debt Securities, Available-for-sale, Unrealized Loss Position	5,072,887
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	383,768	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	2,176,299
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	65,646
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,239,828
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	872,087
Debt Securities, Available-for-sale, Unrealized Loss Position	6,416,127
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	937,733	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	3,391,385
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	45,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,543,520
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	250,537
Debt Securities, Available-for-sale, Unrealized Loss Position	4,934,905
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 296,177	$ 334,388