Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 4,130,264	$ 4,072,302	$ 3,781,044
Noninterest income	2,061,679	1,856,000	1,851,143
Total income	6,191,943	5,928,302	5,632,187
Provision for credit losses	176,000	132,000	168,000
Amortization of core deposit and other intangible assets	19,490	24,522	31,366
Depreciation and other amortization	180,924	154,483	165,759
Other noninterest expense	3,268,268	3,109,057	2,943,200
Income before taxes	2,547,261	2,508,240	2,323,862
Income tax expense (benefit)	618,112	590,160	915,556
Net income	1,929,149	1,918,080	1,408,306
Average total assets	119,584,000	116,959,000	120,860,000
Capital expenditures	178,000	98,000	79,000
All Other [Member]
Segment Reporting Information [Line Items]
Net interest income	537,940	557,542	410,928
Noninterest income	695,443	651,439	609,945
Total income	1,233,383	1,208,981	1,020,873
Provision for credit losses	6,257	(8,128)	8,265
Amortization of core deposit and other intangible assets	18,430	23,462	30,306
Depreciation and other amortization	68,840	68,004	69,923
Other noninterest expense	1,157,432	1,125,428	1,019,465
Income before taxes	(17,576)	215	(107,086)
Income tax expense (benefit)	(28,625)	(54,766)	(40,752)
Net income	11,049	54,981	(66,334)
Average total assets	14,953,000	13,877,000	13,684,000
Capital expenditures	98,000	65,000	44,000
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	451,307	434,579	393,948
Noninterest income	113,855	111,600	112,512
Total income	565,162	546,179	506,460
Provision for credit losses	16,501	10,916	15,598
Depreciation and other amortization	412	382	393
Other noninterest expense	319,136	305,340	294,493
Income before taxes	229,113	229,541	195,976
Income tax expense (benefit)	60,617	61,279	80,043
Net income	168,496	168,262	115,933
Average total assets	5,793,000	5,631,000	5,602,000
Capital expenditures	1,000
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	828,888	821,812	809,301
Noninterest income	289,558	288,908	283,447
Total income	1,118,446	1,110,720	1,092,748
Provision for credit losses	25,580	8,976	11,876
Depreciation and other amortization	554	496	509
Other noninterest expense	384,013	364,102	339,936
Income before taxes	708,299	737,146	740,427
Income tax expense (benefit)	187,835	198,229	303,556
Net income	520,464	538,917	436,871
Average total assets	28,142,000	26,626,000	26,573,000
Capital expenditures	2,000
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	692,526	665,220	649,378
Noninterest income	214,970	183,955	169,966
Total income	907,496	849,175	819,344
Provision for credit losses	1,537	3,159	(7,524)
Amortization of core deposit and other intangible assets	1,060	1,060	1,060
Depreciation and other amortization	25,560	25,852	24,410
Other noninterest expense	240,736	217,387	207,493
Income before taxes	638,603	601,717	593,905
Income tax expense (benefit)	152,977	148,807	229,770
Net income	485,626	452,910	364,135
Average total assets	23,921,000	22,885,000	22,741,000
Capital expenditures			1,000
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	209,807	228,051	277,095
Noninterest income	26,919	(9,690)	23,851
Total income	236,726	218,361	300,946
Provision for credit losses	3,608	6,683	31,119
Depreciation and other amortization	263	187	279
Other noninterest expense	52,901	65,393	76,021
Income before taxes	179,954	146,098	193,527
Income tax expense (benefit)	36,342	29,872	58,559
Net income	143,612	116,226	134,968
Average total assets	29,081,000	32,123,000	37,203,000
Capital expenditures		1,000
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	20,008	13,933	30,328
Noninterest income	393,372	305,560	321,589
Total income	413,380	319,493	351,917
Provision for credit losses	382	(2,178)	1,254
Depreciation and other amortization	46,901	24,288	32,011
Other noninterest expense	274,414	241,624	247,639
Income before taxes	91,683	55,759	71,013
Income tax expense (benefit)	19,355	10,272	25,446
Net income	72,328	45,487	45,567
Average total assets	2,611,000	2,161,000	2,355,000
Capital expenditures	1,000	1,000
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	1,389,788	1,351,165	1,210,066
Noninterest income	327,562	324,228	329,833
Total income	1,717,350	1,675,393	1,539,899
Provision for credit losses	122,135	112,572	107,412
Depreciation and other amortization	38,394	35,274	38,234
Other noninterest expense	839,636	789,783	758,153
Income before taxes	717,185	737,764	636,100
Income tax expense (benefit)	189,611	196,467	258,934
Net income	527,574	541,297	377,166
Average total assets	15,083,000	13,656,000	12,702,000
Capital expenditures	$ 76,000	$ 31,000	$ 34,000