Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net interest income	$ 2,842,587	$ 2,676,446	$ 2,673,229
Noninterest income	1,825,037	1,779,273	1,865,205
Total income	4,667,624	4,455,719	4,538,434
Provision for credit losses	170,000	124,000	185,000
Amortization of core deposit and other intangible assets	26,424	33,824	46,912
Depreciation and other amortization	148,925	164,906	156,823
Other noninterest expense	2,647,583	2,490,744	2,384,131
Income (loss) before taxes	1,674,692	1,642,245	1,765,568
Income tax expense (benefit)	595,025	575,999	627,088
Net income (loss)	1,079,667	1,066,246	1,138,480
Average total assets	101,780,000	92,143,000	83,662,000
Capital expenditures	82,000	73,000	130,000
All Other [Member]
Segment Reporting Information [Line Items]
Net interest income	105,143	(21,543)	(183,361)
Noninterest income	594,586	599,870	672,576
Total income	699,729	578,327	489,215
Provision for credit losses	62,074	(12,954)	(3,679)
Amortization of core deposit and other intangible assets	26,424	33,824	46,912
Depreciation and other amortization	64,852	61,848	57,120
Other noninterest expense	959,345	854,883	713,873
Income (loss) before taxes	(412,966)	(359,274)	(325,011)
Income tax expense (benefit)	(213,682)	(201,119)	(180,238)
Net income (loss)	(199,284)	(158,155)	(144,773)
Average total assets	12,870,000	12,277,000	9,262,000
Capital expenditures	68,000	57,000	89,000
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		84,542	92,323
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	63,939	67,482	83,574
Noninterest income	336,099	331,366	325,454
Total income	400,038	398,848	409,028
Provision for credit losses	(5,225)	(1,508)	(10,906)
Depreciation and other amortization	27,883	47,086	48,698
Other noninterest expense	233,651	216,556	221,984
Income (loss) before taxes	143,729	136,714	149,252
Income tax expense (benefit)	55,151	52,172	56,929
Net income (loss)	88,578	84,542	92,323
Average total assets	2,918,000	3,076,000	2,651,000
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		273,358	320,950
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	917,041	908,828	962,214
Noninterest income	324,953	336,042	373,628
Total income	1,241,994	1,244,870	1,335,842
Provision for credit losses	72,953	77,158	72,502
Depreciation and other amortization	35,291	37,788	34,599
Other noninterest expense	682,594	668,919	687,275
Income (loss) before taxes	451,156	461,005	541,466
Income tax expense (benefit)	183,638	187,647	220,516
Net income (loss)	267,518	273,358	320,950
Average total assets	11,035,000	10,449,000	10,997,000
Capital expenditures	14,000	14,000	40,000
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		99,270	101,065
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	338,855	345,773	365,786
Noninterest income	108,195	105,149	102,613
Total income	447,050	450,922	468,399
Provision for credit losses	15,513	18,883	26,550
Depreciation and other amortization	407	405	198
Other noninterest expense	264,163	263,734	270,759
Income (loss) before taxes	166,967	167,900	170,892
Income tax expense (benefit)	68,209	68,630	69,827
Net income (loss)	98,758	99,270	101,065
Average total assets	5,339,000	5,278,000	5,107,000
Capital expenditures		2,000	1,000
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		402,928	407,393
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	753,604	746,344	785,987
Noninterest income	290,142	254,295	263,925
Total income	1,043,746	1,000,639	1,049,912
Provision for credit losses	25,089	33,213	76,791
Depreciation and other amortization	566	588	564
Other noninterest expense	288,303	284,091	289,582
Income (loss) before taxes	729,788	682,747	682,975
Income tax expense (benefit)	298,758	279,819	275,582
Net income (loss)	431,030	402,928	407,393
Average total assets	24,143,000	22,860,000	21,710,000
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)		315,960	329,286
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	577,922	555,358	590,009
Noninterest income	142,948	125,087	130,833
Total income	720,870	680,445	720,842
Provision for credit losses	(8,003)	(7,339)	6,613
Depreciation and other amortization	19,247	16,300	14,314
Other noninterest expense	169,688	169,039	173,345
Income (loss) before taxes	539,938	502,445	526,570
Income tax expense (benefit)	199,297	186,485	197,284
Net income (loss)	340,641	315,960	329,286
Average total assets	18,827,000	17,405,000	17,305,000
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)		48,343	32,236
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	86,083	74,204	69,020
Noninterest income	28,114	27,464	(3,824)
Total income	114,197	101,668	65,196
Provision for credit losses	7,599	16,547	17,129
Depreciation and other amortization	679	891	1,330
Other noninterest expense	49,839	33,522	27,313
Income (loss) before taxes	56,080	50,708	19,424
Income tax expense (benefit)	3,654	2,365	(12,812)
Net income (loss)	52,426	48,343	32,236
Average total assets	$ 26,648,000	$ 20,798,000	$ 16,630,000