Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Income Statement Data Abstract
Net interest income	$ 176,717	$ 166,488	$ 348,704	$ 334,301
Noninterest income	82,168	86,482	165,360	166,295
Total income	258,885	252,970	514,064	500,596
Provision for credit losses	14,000	5,000	34,000	9,500
Noninterest expense	174,360	176,777	348,331	350,769
Income before income taxes	70,525	71,193	131,733	140,327
Income tax expense	21,434	21,793	40,108	44,255
Net income	$ 49,091	$ 49,400	$ 91,625	$ 96,072
Return on average allocated capital (ROCET1)	9.90%	10.50%	9.20%	10.40%
Segment Balance Sheet Data
Average earning assets	$ 25,968,049	$ 24,266,367	$ 25,620,211	$ 24,207,523
Average loans	19,641,985	18,188,305	19,282,408	18,002,741
Average deposits	20,288,953	19,626,210	20,431,966	19,342,281
Average allocated capital (CET1)	1,913,241	1,819,819	1,904,861	1,812,061
Operating Segments [Member] | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	80,069	76,155	159,233	151,846
Noninterest income	10,936	12,305	22,549	24,918
Total income	91,005	88,460	181,782	176,764
Provision for credit losses	15,114	9,935	27,853	19,460
Noninterest expense	37,140	34,889	71,543	69,350
Income before income taxes	38,751	43,636	82,386	87,954
Income tax expense	13,137	15,061	27,716	30,429
Net income	$ 25,614	$ 28,575	$ 54,670	$ 57,525
Return on average allocated capital (ROCET1)	9.70%	11.80%	10.50%	12.10%
Segment Balance Sheet Data
Average earning assets	$ 10,128,726	$ 9,422,805	$ 9,924,378	$ 9,321,388
Average loans	10,115,959	9,411,245	9,913,591	9,311,672
Average deposits	5,570,919	5,720,064	5,744,533	5,571,627
Average allocated capital (CET1)	1,067,203	968,690	1,049,431	955,799
Operating Segments [Member] | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	84,969	87,385	170,574	173,742
Noninterest income	65,132	69,530	128,880	134,874
Total income	150,101	156,915	299,454	308,616
Provision for credit losses	6,246	6,592	12,388	13,663
Noninterest expense	121,965	125,387	243,260	243,760
Income before income taxes	21,890	24,936	43,806	51,193
Income tax expense	7,662	8,728	15,332	17,918
Net income	$ 14,228	$ 16,208	$ 28,474	$ 33,275
Return on average allocated capital (ROCET1)	9.00%	10.20%	9.10%	10.40%
Segment Balance Sheet Data
Average earning assets	$ 9,325,036	$ 8,709,691	$ 9,222,677	$ 8,618,054
Average loans	9,323,720	8,709,691	9,221,370	8,618,054
Average deposits	11,331,214	10,862,330	11,215,704	10,693,412
Average allocated capital (CET1)	633,829	640,256	630,520	643,796
Operating Segments [Member] | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	11,679	2,948	18,897	8,713
Noninterest income	6,100	4,647	13,931	6,503
Total income	17,779	7,595	32,828	15,216
Provision for credit losses	(7,360)	(11,527)	(6,241)	(23,623)
Noninterest expense	15,255	16,501	33,528	37,659
Income before income taxes	9,884	2,621	5,541	1,180
Income tax expense	635	(1,996)	(2,940)	(4,092)
Net income	$ 9,249	$ 4,617	$ 8,481	$ 5,272
Return on average allocated capital (ROCET1)	13.40%	5.80%	3.70%	2.40%
Segment Balance Sheet Data
Average earning assets	$ 6,514,287	$ 6,133,871	$ 6,473,156	$ 6,268,081
Average loans	202,306	67,369	147,447	73,015
Average deposits	3,386,820	3,043,816	3,471,729	3,077,242
Average allocated capital (CET1)	$ 212,209	$ 210,873	$ 224,910	$ 212,466