Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,444	$ 1,017,198	$ 988,997
Provision for credit losses	176,000	132,000	168,000
Net charge-offs
Charge-offs	(237,708)	(231,241)	(224,598)
Recoveries	93,335	101,487	84,799
Net (charge-offs) recoveries	(144,373)	(129,754)	(139,799)
Ending balance	1,051,071	1,019,444	1,017,198
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	330,055	328,599	330,833
Provision for credit losses	69,702	33,967	41,511
Net charge-offs
Charge-offs	(58,244)	(60,414)	(64,941)
Recoveries	24,581	27,903	21,196
Net (charge-offs) recoveries	(33,663)	(32,511)	(43,745)
Ending balance	366,094	330,055	328,599
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	341,655	374,085	362,719
Provision for credit losses	(10,726)	(41,181)	6,715
Net charge-offs
Charge-offs	(12,664)	(12,286)	(7,931)
Recoveries	3,936	21,037	12,582
Net (charge-offs) recoveries	(8,728)	8,751	4,651
Ending balance	322,201	341,655	374,085
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	69,125	65,405	61,127
Provision for credit losses	(8,585)	12,401	16,094
Net charge-offs
Charge-offs	(12,711)	(15,345)	(20,799)
Recoveries	8,204	6,664	8,983
Net (charge-offs) recoveries	(4,507)	(8,681)	(11,816)
Ending balance	56,033	69,125	65,405
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	200,564	170,809	156,288
Provision for credit losses	126,029	127,068	103,410
Net charge-offs
Charge-offs	(154,089)	(143,196)	(130,927)
Recoveries	56,614	45,883	42,038
Net (charge-offs) recoveries	(97,475)	(97,313)	(88,889)
Ending balance	229,118	200,564	170,809
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,045	78,300	78,030
Provision for credit losses	(420)	(255)	270
Net charge-offs
Ending balance	$ 77,625	$ 78,045	$ 78,300