Business Segment Information - Amounts Of Consolidated Revenue, Expense, Tax And Assets (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Segment Reporting, Measurement Disclosures [Abstract]
Number of operating segments | segment					4
Segment Reporting Information [Line Items]
Net interest income	$ 303,610		$ 310,932		$ 598,118	$ 612,105
Provision/(provision credit) for loan losses	13,000		0		22,000	(1,000)
Noninterest income	157,993		127,525		299,038	263,542
Noninterest expense	300,394		332,768		596,484	646,033
Income/(loss) before income taxes	148,209		105,689		278,672	230,614
Provision/(benefit) for income taxes	34,467		19,697		61,525	49,628
Net income/(loss)	113,742	$ 103,405	85,992	$ 94,994	217,147	180,986
Average assets	41,243,007		40,173,712		41,064,093	40,261,729
Expenses associated with rebranding initiatives	9,100				9,100
Regional Banking
Segment Reporting Information [Line Items]
Net interest income	297,328		305,935		583,241	598,084
Provision/(provision credit) for loan losses	17,775		4,613		31,218	8,950
Noninterest income	81,475		80,767		154,505	161,055
Noninterest expense	193,268		210,038		392,736	412,712
Income/(loss) before income taxes	167,760		172,051		313,792	337,477
Provision/(benefit) for income taxes	39,504		40,424		73,364	79,387
Net income/(loss)	128,256		131,627		240,428	258,090
Average assets	30,209,191		28,401,733		29,513,197	28,231,978
Fixed Income
Segment Reporting Information [Line Items]
Net interest income	6,171		9,200		13,502	17,688
Noninterest income	65,622		38,363		119,429	83,967
Noninterest expense	55,770		46,933		106,544	96,296
Income/(loss) before income taxes	16,023		630		26,387	5,359
Provision/(benefit) for income taxes	3,781		(69)		6,178	970
Net income/(loss)	12,242		699		20,209	4,389
Average assets	3,127,333		3,247,620		2,988,575	3,361,438
Corporate
Segment Reporting Information [Line Items]
Net interest income	(7,000)		(17,177)		(14,803)	(33,373)
Noninterest income	9,400		8,738		22,752	18,054
Noninterest expense	55,500		67,868		95,874	121,218
Income/(loss) before income taxes	(53,100)		(76,307)		(87,925)	(136,537)
Provision/(benefit) for income taxes	(13,150)		(22,960)		(24,546)	(36,739)
Net income/(loss)	(39,950)		(53,347)		(63,379)	(99,798)
Average assets	6,814,261		6,963,450		7,428,906	7,039,301
Non-Strategic
Segment Reporting Information [Line Items]
Net interest income	7,111		12,974		16,178	29,706
Provision/(provision credit) for loan losses	(4,775)		(4,613)		(9,218)	(9,950)
Noninterest income	1,496		(343)		2,352	466
Noninterest expense	(4,144)		7,929		1,330	15,807
Income/(loss) before income taxes	17,526		9,315		26,418	24,315
Provision/(benefit) for income taxes	4,332		2,302		6,529	6,010
Net income/(loss)	13,194		7,013		19,889	18,305
Average assets	$ 1,092,222		$ 1,560,909		$ 1,133,415	$ 1,629,012