Segment Reporting Selected Segment Income Statement and Balance Sheet Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Income Statement Data Abstract
Net interest income	$ 170,509	$ 172,630	$ 504,810	$ 506,306
Noninterest income	79,916	74,908	246,513	220,676
Total revenue	250,425	247,538	751,323	726,982
Credit provision	8,000	1,000	17,500	11,000
Noninterest expense	171,436	171,853	522,507	507,436
Income before income taxes	70,989	74,685	211,316	208,546
Income tax expense (benefit)	21,551	24,478	65,806	66,775
Net income	$ 49,438	$ 50,207	$ 145,510	$ 141,771
Return on average allocated capital (ROTICE)	10.20%	10.40%	10.30%	9.80%
Segment Balance Sheet Data
Average earning assets	$ 24,834,014	$ 23,096,717	$ 24,418,648	$ 22,513,323
Average loans	18,452,749	17,140,961	18,154,392	16,654,233
Average deposits	20,293,599	17,873,378	19,662,872	17,348,729
Average allocated capital (TICE)	1,837,436	1,871,246	1,820,612	1,887,412
Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	78,283	72,474	230,130	220,973
Noninterest income	11,305	11,888	36,222	35,971
Total revenue	89,588	84,362	266,352	256,944
Credit provision	10,851	11,074	30,312	37,021
Noninterest expense	37,293	35,044	106,643	110,558
Income before income taxes	41,444	38,244	129,397	109,365
Income tax expense (benefit)	13,955	12,343	44,384	35,767
Net income	$ 27,489	$ 25,901	$ 85,013	$ 73,598
Return on average allocated capital (ROTICE)	11.00%	13.80%	11.80%	12.80%
Segment Balance Sheet Data
Average earning assets	$ 9,475,469	$ 8,761,870	$ 9,373,312	$ 8,933,616
Average loans	9,466,761	8,750,207	9,363,936	8,922,631
Average deposits	6,044,306	5,092,314	5,730,918	5,129,046
Average allocated capital (TICE)	988,283	744,792	966,746	766,391
Community, Consumer, and Business [Member]
Segment Income Statement Data Abstract
Net interest income	88,209	82,067	261,951	227,409
Noninterest income	64,911	54,601	200,042	168,287
Total revenue	153,120	136,668	461,993	395,696
Credit provision	5,963	6,773	19,625	16,534
Noninterest expense	122,393	122,722	366,410	346,084
Income before income taxes	24,764	7,173	75,958	33,078
Income tax expense (benefit)	8,667	2,467	26,585	11,388
Net income	$ 16,097	$ 4,706	$ 49,373	$ 21,690
Return on average allocated capital (ROTICE)	10.10%	3.20%	10.30%	5.40%
Segment Balance Sheet Data
Average earning assets	$ 8,917,831	$ 8,310,839	$ 8,719,078	$ 7,646,487
Average loans	8,917,831	8,310,839	8,719,078	7,646,487
Average deposits	10,969,172	10,337,637	10,786,342	9,872,624
Average allocated capital (TICE)	632,878	583,096	640,116	535,528
Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	4,017	18,089	12,729	57,924
Noninterest income	3,700	8,419	10,249	16,418
Total revenue	7,717	26,508	22,978	74,342
Credit provision	(8,814)	(16,847)	(32,437)	(42,555)
Noninterest expense	11,750	14,087	49,454	50,794
Income before income taxes	4,781	29,268	5,961	66,103
Income tax expense (benefit)	(1,071)	9,668	(5,163)	19,620
Net income	$ 5,852	$ 19,600	$ 11,124	$ 46,483
Return on average allocated capital (ROTICE)	6.70%	13.40%	3.90%	9.80%
Segment Balance Sheet Data
Average earning assets	$ 6,440,714	$ 6,024,008	$ 6,326,258	$ 5,933,220
Average loans	68,157	79,915	71,378	85,115
Average deposits	3,280,121	2,443,427	3,145,612	2,347,059
Average allocated capital (TICE)	$ 216,275	$ 543,358	$ 213,750	$ 585,493