Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income	$ 3,469,887	$ 2,842,587	$ 2,676,446
Noninterest income	1,825,996	1,825,037	1,779,273
Total income	5,295,883	4,667,624	4,455,719
Provision for credit losses	190,000	170,000	124,000
Amortization of core deposit and other intangible assets	42,613	26,424	33,824
Depreciation and other amortization	157,978	148,925	164,906
Other noninterest expense	2,846,894	2,647,583	2,490,744
Income before taxes	2,058,398	1,674,692	1,642,245
Income tax expense (benefit)	743,284	595,025	575,999
Net income	1,315,114	1,079,667	1,066,246
Average total assets	124,340,000	101,780,000	92,143,000
Capital expenditures	108,000	82,000	73,000
All Other [Member]
Segment Reporting Information [Line Items]
Net interest income	230,589	93,600	(21,543)
Noninterest income	570,475	594,586	599,870
Total income	801,064	688,186	578,327
Provision for credit losses	(3,910)	62,074	(12,954)
Amortization of core deposit and other intangible assets	42,613	26,424	33,824
Depreciation and other amortization	68,541	64,852	61,848
Other noninterest expense	892,625	959,345	854,883
Income before taxes	(198,805)	(424,509)	(359,274)
Income tax expense (benefit)	(140,657)	(218,379)	(201,119)
Net income	(58,148)	(206,130)	(158,155)
Average total assets	16,885,000	12,870,000	12,277,000
Capital expenditures	62,000	68,000	57,000
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	354,333	338,855	345,773
Noninterest income	108,783	108,195	105,149
Total income	463,116	447,050	450,922
Provision for credit losses	12,709	15,513	18,883
Depreciation and other amortization	404	407	405
Other noninterest expense	292,124	264,163	263,734
Income before taxes	157,879	166,967	167,900
Income tax expense (benefit)	64,533	68,209	68,630
Net income	93,346	98,758	99,270
Average total assets	5,456,000	5,339,000	5,278,000
Capital expenditures			2,000
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	785,874	753,604	746,344
Noninterest income	274,923	290,142	254,295
Total income	1,060,797	1,043,746	1,000,639
Provision for credit losses	34,903	25,089	33,213
Depreciation and other amortization	520	566	588
Other noninterest expense	327,616	288,303	284,091
Income before taxes	697,758	729,788	682,747
Income tax expense (benefit)	286,062	298,758	279,819
Net income	411,696	431,030	402,928
Average total assets	25,592,000	24,143,000	22,860,000
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	608,385	577,922	555,358
Noninterest income	179,706	142,948	125,087
Total income	788,091	720,870	680,445
Provision for credit losses	(3,447)	(8,003)	(7,339)
Depreciation and other amortization	20,120	19,247	16,300
Other noninterest expense	204,965	169,688	169,039
Income before taxes	566,453	539,938	502,445
Income tax expense (benefit)	216,095	199,297	186,485
Net income	350,358	340,641	315,960
Average total assets	21,131,000	18,827,000	17,405,000
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	345,926	97,626	74,204
Noninterest income	26,075	28,114	27,464
Total income	372,001	125,740	101,668
Provision for credit losses	32,925	7,599	16,547
Depreciation and other amortization	472	679	891
Other noninterest expense	95,300	49,839	33,522
Income before taxes	243,304	67,623	50,708
Income tax expense (benefit)	79,766	8,351	2,365
Net income	163,538	59,272	48,343
Average total assets	40,867,000	26,648,000	20,798,000
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	70,655	63,939	67,482
Noninterest income	342,858	336,099	331,366
Total income	413,513	400,038	398,848
Provision for credit losses	(3,617)	(5,225)	(1,508)
Depreciation and other amortization	30,264	27,883	47,086
Other noninterest expense	258,141	233,651	216,556
Income before taxes	128,725	143,729	136,714
Income tax expense (benefit)	49,047	55,151	52,172
Net income	79,678	88,578	84,542
Average total assets	2,569,000	2,918,000	3,076,000
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	1,074,125	917,041	908,828
Noninterest income	323,176	324,953	336,042
Total income	1,397,301	1,241,994	1,244,870
Provision for credit losses	120,437	72,953	77,158
Depreciation and other amortization	37,657	35,291	37,788
Other noninterest expense	776,123	682,594	668,919
Income before taxes	463,084	451,156	461,005
Income tax expense (benefit)	188,438	183,638	187,647
Net income	274,646	267,518	273,358
Average total assets	11,840,000	11,035,000	10,449,000
Capital expenditures	$ 46,000	$ 14,000	$ 14,000