Securities - Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Held to Maturity, Due in one year or less, Amortized Cost	$ 59,282
Held to Maturity, Due after one year through five years, Amortized Cost	15,524
Held to Maturity, Due after five years through ten years, Amortized Cost	551,088
Held to Maturity, Due after ten years, Amortized Cost	3,065,593
Held to Maturity, Amortized Cost	3,691,487	$ 2,639,241
Held to Maturity, Due in one year or less, Estimated Fair Value	59,242
Held to Maturity, Due after one year through five years, Estimated Fair Value	15,380
Held to Maturity, Due after five years through ten years, Estimated Fair Value	487,459
Held to Maturity, Due after ten years, Estimated Fair Value	2,981,848
Held to Maturity, Estimated Fair Value	3,543,929	2,467,865
Available-for-sale Securities, Due in one year or less, Amortized Cost	1,725,618
Available for Sale, Due after one year through five years, Amortized Cost	2,864,894
Available for Sale, Due after five years through ten years, Amortized Cost	2,283,180
Available for Sale, Due after ten years, Amortized Cost	11,944,462
Debt Securities, Available-for-sale, Amortized Cost	18,860,732	19,908,432
Available for Sale, Due in one year or less, Estimated Fair Value	1,696,603
Available for Sale, Due after one year through five years, Estimated Fair Value	2,740,369
Available for Sale, Due after five years through ten years, Estimated Fair Value	2,077,949
Available for Sale, Due after ten years, Estimated Fair Value	10,691,758
Securities available for sale, at estimated fair value	17,249,257	18,243,605
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Due in one year or less, Amortized Cost	1,286,197
Available for Sale, Due after one year through five years, Amortized Cost	2,542,538
Available for Sale, Due after five years through ten years, Amortized Cost	1,435,692
Available for Sale, Due after ten years, Amortized Cost	192,229
Debt Securities, Available-for-sale, Amortized Cost	5,456,656	5,450,546
Available for Sale, Due in one year or less, Estimated Fair Value	1,257,329
Available for Sale, Due after one year through five years, Estimated Fair Value	2,420,131
Available for Sale, Due after five years through ten years, Estimated Fair Value	1,250,420
Available for Sale, Due after ten years, Estimated Fair Value	145,008
Securities available for sale, at estimated fair value	5,072,888	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	513,530
Held to Maturity, Due after ten years, Amortized Cost	752,288
Held to Maturity, Amortized Cost	1,265,818	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	450,850
Held to Maturity, Due after ten years, Estimated Fair Value	742,682
Held to Maturity, Estimated Fair Value	1,193,532	460,800
Available-for-sale Securities, Due in one year or less, Amortized Cost	310
Available for Sale, Due after one year through five years, Amortized Cost	4,985
Available for Sale, Due after five years through ten years, Amortized Cost	15,986
Available for Sale, Due after ten years, Amortized Cost	7,704,122
Debt Securities, Available-for-sale, Amortized Cost	7,725,403	7,316,824
Available for Sale, Due in one year or less, Estimated Fair Value	305
Available for Sale, Due after one year through five years, Estimated Fair Value	4,865
Available for Sale, Due after five years through ten years, Estimated Fair Value	15,898
Available for Sale, Due after ten years, Estimated Fair Value	6,771,707
Securities available for sale, at estimated fair value	6,792,775	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	59,282
Held to Maturity, Due after one year through five years, Amortized Cost	14,024
Held to Maturity, Due after five years through ten years, Amortized Cost	37,558
Held to Maturity, Due after ten years, Amortized Cost	2,313,305
Held to Maturity, Amortized Cost	2,424,169	2,111,619
Held to Maturity, Due in one year or less, Estimated Fair Value	59,242
Held to Maturity, Due after one year through five years, Estimated Fair Value	13,949
Held to Maturity, Due after five years through ten years, Estimated Fair Value	36,609
Held to Maturity, Due after ten years, Estimated Fair Value	2,239,166
Held to Maturity, Estimated Fair Value	2,348,966	2,005,634
Available-for-sale Securities, Due in one year or less, Amortized Cost	439,111
Available for Sale, Due after one year through five years, Amortized Cost	317,371
Available for Sale, Due after five years through ten years, Amortized Cost	831,502
Available for Sale, Due after ten years, Amortized Cost	4,048,111
Debt Securities, Available-for-sale, Amortized Cost	5,636,095	7,098,635
Available for Sale, Due in one year or less, Estimated Fair Value	438,969
Available for Sale, Due after one year through five years, Estimated Fair Value	315,373
Available for Sale, Due after five years through ten years, Estimated Fair Value	811,631
Available for Sale, Due after ten years, Estimated Fair Value	3,775,043
Securities available for sale, at estimated fair value	5,341,016	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	1,431
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	1,431	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	42,578	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	$ 42,578	$ 42,427