Securities - Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Held to Maturity, Due in one year or less, Amortized Cost	$ 72,953
Held to Maturity, Due after one year through five years, Amortized Cost	19,342
Held to Maturity, Due after five years through ten years, Amortized Cost	535,509
Held to Maturity, Due after ten years, Amortized Cost	3,084,037
Held to Maturity, Amortized Cost	3,711,841	$ 2,639,241
Held to Maturity, Due in one year or less, Estimated Fair Value	72,976
Held to Maturity, Due after one year through five years, Estimated Fair Value	19,259
Held to Maturity, Due after five years through ten years, Estimated Fair Value	480,259
Held to Maturity, Due after ten years, Estimated Fair Value	3,029,263
Held to Maturity, Estimated Fair Value	3,601,757	2,467,865
Available-for-sale Securities, Due in one year or less, Amortized Cost	1,555,297
Available for Sale, Due after one year through five years, Amortized Cost	3,381,099
Available for Sale, Due after five years through ten years, Amortized Cost	2,305,268
Available for Sale, Due after ten years, Amortized Cost	12,102,248
Debt Securities, Available-for-sale, Amortized Cost	19,386,409	19,908,432
Available for Sale, Due in one year or less, Estimated Fair Value	1,521,506
Available for Sale, Due after one year through five years, Estimated Fair Value	3,296,931
Available for Sale, Due after five years through ten years, Estimated Fair Value	2,135,038
Available for Sale, Due after ten years, Estimated Fair Value	10,985,858
Securities available for sale, at estimated fair value	17,981,830	18,243,605
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Due in one year or less, Amortized Cost	1,286,682
Available for Sale, Due after one year through five years, Amortized Cost	2,539,671
Available for Sale, Due after five years through ten years, Amortized Cost	1,435,094
Available for Sale, Due after ten years, Amortized Cost	192,138
Debt Securities, Available-for-sale, Amortized Cost	5,453,585	5,450,546
Available for Sale, Due in one year or less, Estimated Fair Value	1,251,908
Available for Sale, Due after one year through five years, Estimated Fair Value	2,451,237
Available for Sale, Due after five years through ten years, Estimated Fair Value	1,275,631
Available for Sale, Due after ten years, Estimated Fair Value	149,320
Securities available for sale, at estimated fair value	5,128,096	5,051,587
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	0
Held to Maturity, Due after five years through ten years, Amortized Cost	513,796
Held to Maturity, Due after ten years, Amortized Cost	759,283
Held to Maturity, Amortized Cost	1,273,079	526,122
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	0
Held to Maturity, Due after five years through ten years, Estimated Fair Value	459,002
Held to Maturity, Due after ten years, Estimated Fair Value	761,208
Held to Maturity, Estimated Fair Value	1,220,210	460,800
Available-for-sale Securities, Due in one year or less, Amortized Cost	8
Available for Sale, Due after one year through five years, Amortized Cost	6,422
Available for Sale, Due after five years through ten years, Amortized Cost	17,165
Available for Sale, Due after ten years, Amortized Cost	7,834,074
Debt Securities, Available-for-sale, Amortized Cost	7,857,669	7,316,824
Available for Sale, Due in one year or less, Estimated Fair Value	8
Available for Sale, Due after one year through five years, Estimated Fair Value	6,340
Available for Sale, Due after five years through ten years, Estimated Fair Value	17,181
Available for Sale, Due after ten years, Estimated Fair Value	6,999,413
Securities available for sale, at estimated fair value	7,022,942	6,376,236
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Due in one year or less, Amortized Cost	72,953
Held to Maturity, Due after one year through five years, Amortized Cost	17,842
Held to Maturity, Due after five years through ten years, Amortized Cost	21,713
Held to Maturity, Due after ten years, Amortized Cost	2,324,754
Held to Maturity, Amortized Cost	2,437,262	2,111,619
Held to Maturity, Due in one year or less, Estimated Fair Value	72,976
Held to Maturity, Due after one year through five years, Estimated Fair Value	17,835
Held to Maturity, Due after five years through ten years, Estimated Fair Value	21,257
Held to Maturity, Due after ten years, Estimated Fair Value	2,268,055
Held to Maturity, Estimated Fair Value	2,380,123	2,005,634
Available-for-sale Securities, Due in one year or less, Amortized Cost	268,607
Available for Sale, Due after one year through five years, Amortized Cost	835,006
Available for Sale, Due after five years through ten years, Amortized Cost	853,009
Available for Sale, Due after ten years, Amortized Cost	4,076,036
Debt Securities, Available-for-sale, Amortized Cost	6,032,658	7,098,635
Available for Sale, Due in one year or less, Estimated Fair Value	269,590
Available for Sale, Due after one year through five years, Estimated Fair Value	839,354
Available for Sale, Due after five years through ten years, Estimated Fair Value	842,226
Available for Sale, Due after ten years, Estimated Fair Value	3,837,125
Securities available for sale, at estimated fair value	5,788,295	6,773,355
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	1,424
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	1,424	1,431
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	42,497	42,427
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	$ 42,497	$ 42,427