v3.25.2
Securities - Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity (Detail) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Held to Maturity, Due in one year or less, Amortized Cost $ 6,445  
Held to Maturity, Due after one year through five years, Amortized Cost 527,583  
Held to Maturity, Due after five years through ten years, Amortized Cost 80,897  
Held to Maturity, Due after ten years, Amortized Cost 2,871,675  
Held to Maturity, Amortized Cost 3,486,600 $ 3,534,085
Held to Maturity, Due in one year or less, Estimated Fair Value 6,467  
Held to Maturity, Due after one year through five years, Estimated Fair Value 492,746  
Held to Maturity, Due after five years through ten years, Estimated Fair Value 77,212  
Held to Maturity, Due after ten years, Estimated Fair Value 2,641,784  
Held to Maturity, Estimated Fair Value 3,218,209 3,360,546
Available-for-sale Securities, Due in one year or less, Amortized Cost 774,376  
Available for Sale, Due after one year through five years, Amortized Cost 2,285,324  
Available for Sale, Due after five years through ten years, Amortized Cost 957,816  
Available for Sale, Due after ten years, Amortized Cost 13,969,260  
Debt Securities, Available-for-sale, Amortized Cost 18,030,136 16,602,158
Available for Sale, Due in one year or less, Estimated Fair Value 770,008  
Available for Sale, Due after one year through five years, Estimated Fair Value 2,185,309  
Available for Sale, Due after five years through ten years, Estimated Fair Value 898,446  
Available for Sale, Due after ten years, Estimated Fair Value 12,715,563  
Securities available for sale, at estimated fair value 16,612,686 15,043,625
US Treasury Securities [Member]    
Schedule of Investments [Line Items]    
Available-for-sale Securities, Due in one year or less, Amortized Cost 697,559  
Available for Sale, Due after one year through five years, Amortized Cost 1,935,177  
Available for Sale, Due after five years through ten years, Amortized Cost 198,253  
Available for Sale, Due after ten years, Amortized Cost 192,972  
Debt Securities, Available-for-sale, Amortized Cost 3,023,961 3,692,215
Available for Sale, Due in one year or less, Estimated Fair Value 693,221  
Available for Sale, Due after one year through five years, Estimated Fair Value 1,837,015  
Available for Sale, Due after five years through ten years, Estimated Fair Value 172,984  
Available for Sale, Due after ten years, Estimated Fair Value 137,719  
Securities available for sale, at estimated fair value 2,840,939 3,442,320
Residential Mortgage Backed Securities [Member]    
Schedule of Investments [Line Items]    
Held to Maturity, Due in one year or less, Amortized Cost 0  
Held to Maturity, Due after one year through five years, Amortized Cost 508,570  
Held to Maturity, Due after five years through ten years, Amortized Cost 11,232  
Held to Maturity, Due after ten years, Amortized Cost 640,884  
Held to Maturity, Amortized Cost 1,160,686 1,193,840
Held to Maturity, Due in one year or less, Estimated Fair Value 0  
Held to Maturity, Due after one year through five years, Estimated Fair Value 473,543  
Held to Maturity, Due after five years through ten years, Estimated Fair Value 9,570  
Held to Maturity, Due after ten years, Estimated Fair Value 633,306  
Held to Maturity, Estimated Fair Value 1,116,419 1,122,764
Available-for-sale Securities, Due in one year or less, Amortized Cost 0  
Available for Sale, Due after one year through five years, Amortized Cost 10,157  
Available for Sale, Due after five years through ten years, Amortized Cost 2,453  
Available for Sale, Due after ten years, Amortized Cost 9,704,074  
Debt Securities, Available-for-sale, Amortized Cost 9,716,684 8,024,704
Available for Sale, Due in one year or less, Estimated Fair Value 0  
Available for Sale, Due after one year through five years, Estimated Fair Value 10,161  
Available for Sale, Due after five years through ten years, Estimated Fair Value 2,503  
Available for Sale, Due after ten years, Estimated Fair Value 8,837,599  
Securities available for sale, at estimated fair value 8,850,263 6,997,902
US States and Political Subdivisions Debt Securities [Member]    
Schedule of Investments [Line Items]    
Held to Maturity, Due in one year or less, Amortized Cost 6,445  
Held to Maturity, Due after one year through five years, Amortized Cost 17,513  
Held to Maturity, Due after five years through ten years, Amortized Cost 69,665  
Held to Maturity, Due after ten years, Amortized Cost 2,230,791  
Held to Maturity, Amortized Cost 2,324,414 2,338,745
Held to Maturity, Due in one year or less, Estimated Fair Value 6,467  
Held to Maturity, Due after one year through five years, Estimated Fair Value 17,709  
Held to Maturity, Due after five years through ten years, Estimated Fair Value 67,642  
Held to Maturity, Due after ten years, Estimated Fair Value 2,008,478  
Held to Maturity, Estimated Fair Value 2,100,296 2,236,285
Available-for-sale Securities, Due in one year or less, Amortized Cost 76,817  
Available for Sale, Due after one year through five years, Amortized Cost 339,990  
Available for Sale, Due after five years through ten years, Amortized Cost 757,110  
Available for Sale, Due after ten years, Amortized Cost 4,072,214  
Debt Securities, Available-for-sale, Amortized Cost 5,246,131 4,842,060
Available for Sale, Due in one year or less, Estimated Fair Value 76,787  
Available for Sale, Due after one year through five years, Estimated Fair Value 338,133  
Available for Sale, Due after five years through ten years, Estimated Fair Value 722,959  
Available for Sale, Due after ten years, Estimated Fair Value 3,740,245  
Securities available for sale, at estimated fair value 4,878,124 4,560,224
Other Investments [Member]    
Schedule of Investments [Line Items]    
Held to Maturity, Due in one year or less, Amortized Cost 0  
Held to Maturity, Due after one year through five years, Amortized Cost 1,500  
Held to Maturity, Due after five years through ten years, Amortized Cost 0  
Held to Maturity, Due after ten years, Amortized Cost 0  
Held to Maturity, Amortized Cost 1,500 1,500
Held to Maturity, Due in one year or less, Estimated Fair Value 0  
Held to Maturity, Due after one year through five years, Estimated Fair Value 1,494  
Held to Maturity, Due after five years through ten years, Estimated Fair Value 0  
Held to Maturity, Due after ten years, Estimated Fair Value 0  
Held to Maturity, Estimated Fair Value 1,494 1,497
Available-for-sale Securities, Due in one year or less, Amortized Cost 0  
Available for Sale, Due after one year through five years, Amortized Cost 0  
Available for Sale, Due after five years through ten years, Amortized Cost 0  
Available for Sale, Due after ten years, Amortized Cost 0  
Debt Securities, Available-for-sale, Amortized Cost 43,360 43,179
Available for Sale, Due in one year or less, Estimated Fair Value 0  
Available for Sale, Due after one year through five years, Estimated Fair Value 0  
Available for Sale, Due after five years through ten years, Estimated Fair Value 0  
Available for Sale, Due after ten years, Estimated Fair Value 0  
Securities available for sale, at estimated fair value $ 43,360 $ 43,179