v3.25.2
Securities - Securities Available for Sale, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Schedule of Available-for-Sale Securities [Line Items]    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months $ 2,297,423  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 63,906  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 10,692,778  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 1,387,087  
Debt Securities, Available-for-sale, Unrealized Loss Position 12,990,201  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 1,450,993 $ 1,563,378
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 0  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 2,840,939  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 183,022  
Debt Securities, Available-for-sale, Unrealized Loss Position 2,840,939  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 183,022 249,895
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 1,005,571  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 7,927  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 4,627,613  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 890,406  
Debt Securities, Available-for-sale, Unrealized Loss Position 5,633,184  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 898,333 1,029,154
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 1,291,852  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 55,979  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 3,224,226  
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 313,659  
Debt Securities, Available-for-sale, Unrealized Loss Position 4,516,078  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax $ 369,638 $ 284,329