Business Segment Information - Amounts Of Consolidated Revenue, Expense, Tax And Assets (Details) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting, Measurement Disclosures [Abstract]
Number of operating segments | segment							4
Segment Reporting Information [Line Items]
Net interest income	$ 532,365			$ 300,676			$ 1,140,511	$ 898,794
Provision for credit losses	227,000			14,366			502,388	36,273
Noninterest income	822,923			171,735			1,203,948	470,773
Noninterest expense	587,040			308,306			1,210,139	904,883
Income before income taxes	541,248			149,739			631,932	428,411
Provision for income taxes	2,210			35,796			19,757	97,321
Net income	539,038	$ 56,665	$ 16,472	113,943	$ 113,742	$ 103,405	612,175	331,090
Average assets	81,683,111			41,940,901			57,810,478	41,359,574
Regional Banking
Segment Reporting Information [Line Items]
Net interest income	583,907			302,467			1,233,654	885,932
Provision for credit losses	227,326			19,839			501,453	50,967
Noninterest income	172,457			85,930			333,669	240,555
Noninterest expense	373,680			193,956			768,870	586,697
Income before income taxes	155,358			174,602			297,000	488,823
Provision for income taxes	34,744			41,795			65,497	115,266
Net income	120,614			132,807			231,503	373,557
Average assets	64,371,210			31,632,768			44,170,906	30,231,372
Fixed Income
Segment Reporting Information [Line Items]
Net interest income	11,632			5,309			36,088	18,809
Noninterest income	110,783			77,808			319,741	197,238
Noninterest expense	67,395			67,582			231,488	173,656
Income before income taxes	55,020			15,535			124,341	42,391
Provision for income taxes	13,456			3,707			30,236	10,001
Net income	41,564			11,828			94,105	32,390
Average assets	3,002,282			2,882,478			3,341,255	2,952,925
Corporate
Segment Reporting Information [Line Items]
Net interest income	(69,187)			(13,252)			(145,847)	(28,136)
Noninterest income	539,668			7,359			548,891	30,112
Noninterest expense	142,894			42,297			199,461	139,052
Income before income taxes	327,587			(48,190)			203,583	(137,076)
Provision for income taxes	(46,785)			(11,632)			(77,690)	(36,416)
Net income	374,372			(36,558)			281,273	(100,660)
Average assets	13,595,544			6,434,633			9,527,471	7,098,500
Non-Strategic
Segment Reporting Information [Line Items]
Net interest income	6,013			6,152			16,616	22,189
Provision for credit losses	(326)			(5,473)			935	(14,694)
Noninterest income	15			638			1,647	2,868
Noninterest expense	3,071			4,471			10,320	5,478
Income before income taxes	3,283			7,792			7,008	34,273
Provision for income taxes	795			1,926			1,714	8,470
Net income	2,488			5,866			5,294	25,803
Average assets	$ 714,075			$ 991,022			$ 770,846	$ 1,076,777