Business Segment Information - Amounts Of Consolidated Revenue, Expense, Tax And Assets (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment Reporting, Measurement Disclosures [Abstract]
Number of operating segments | segment					4
Segment Reporting Information [Line Items]
Net interest income	$ 305,344		$ 303,610		$ 608,146	$ 598,118
Provision/(provision credit) for loan losses	110,000		13,000		255,000	22,000
Noninterest income	206,269		157,993		381,025	299,038
Noninterest expense	332,168		300,394		643,487	596,484
Income/(loss) before income taxes	69,445		148,209		90,684	278,672
Provision/(benefit) for income taxes	12,780		34,467		17,547	61,525
Net income/(loss)	56,665	$ 16,472	113,742	$ 103,405	73,137	217,147
Asset impairments, professional fees, and other customer-contact and technology-related expenses			9,100			9,000
Average assets	47,934,074		41,243,007		45,742,993	41,064,093
Regional Banking
Segment Reporting Information [Line Items]
Net interest income	349,749		297,534		649,936	583,636
Provision/(provision credit) for loan losses	108,311		17,776		253,752	31,218
Noninterest income	79,312		81,565		161,208	154,626
Noninterest expense	202,297		192,413		413,331	391,043
Income/(loss) before income taxes	118,453		168,910		144,061	316,001
Provision/(benefit) for income taxes	26,948		39,788		31,349	73,909
Net income/(loss)	91,505		129,122		112,712	242,092
Average assets	35,732,966		30,210,728		33,952,986	29,515,773
Fixed Income
Segment Reporting Information [Line Items]
Net interest income	13,545		6,171		24,459	13,503
Noninterest income	113,235		65,622		208,958	119,429
Noninterest expense	83,039		55,534		164,102	106,067
Income/(loss) before income taxes	43,741		16,259		69,315	26,865
Provision/(benefit) for income taxes	10,679		3,840		16,778	6,297
Net income/(loss)	33,062		12,419		52,537	20,568
Average assets	3,260,362		3,127,305		3,512,277	2,988,548
Corporate
Segment Reporting Information [Line Items]
Net interest income	(63,493)		(7,146)		(76,852)	(15,060)
Noninterest income	12,943		9,401		9,225	22,754
Noninterest expense	43,218		56,873		58,667	98,652
Income/(loss) before income taxes	(93,768)		(54,618)		(126,294)	(90,958)
Provision/(benefit) for income taxes	(25,097)		(13,525)		(31,469)	(25,296)
Net income/(loss)	(68,671)		(41,093)		(94,825)	(65,662)
Average assets	8,168,307		6,827,937		7,476,249	7,439,591
Non-Strategic
Segment Reporting Information [Line Items]
Net interest income	5,543		7,051		10,603	16,039
Provision/(provision credit) for loan losses	1,689		(4,776)		1,248	(9,218)
Noninterest income	779		1,405		1,634	2,229
Noninterest expense	3,614		(4,426)		7,387	722
Income/(loss) before income taxes	1,019		17,658		3,602	26,764
Provision/(benefit) for income taxes	250		4,364		889	6,615
Net income/(loss)	769		13,294		2,713	20,149
Average assets	$ 772,439		$ 1,077,037		$ 801,481	$ 1,120,181