Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,029,867	$ 1,019,248	$ 1,019,444	$ 1,017,198
Provision for credit losses	45,000	16,000	122,000	94,000
Net charge-offs
Charge-offs	(60,241)	(52,066)	(174,747)	(166,265)
Recoveries	23,811	36,306	71,740	74,555
Net (charge-offs) recoveries	(36,430)	(15,760)	(103,007)	(91,710)
Ending balance	1,038,437	1,019,488	1,038,437	1,019,488
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	335,855	328,830	330,055	328,599
Provision for credit losses	24,538	(6,972)	41,146	11,508
Net charge-offs
Charge-offs	(15,678)	(11,792)	(40,786)	(41,273)
Recoveries	6,730	7,123	21,030	18,355
Net (charge-offs) recoveries	(8,948)	(4,669)	(19,756)	(22,918)
Ending balance	351,445	317,189	351,445	317,189
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	343,296	353,761	341,655	374,085
Provision for credit losses	(16,713)	(11,394)	(6,415)	(27,464)
Net charge-offs
Charge-offs	(1,107)	(1,941)	(11,555)	(7,855)
Recoveries	1,656	14,577	3,447	16,237
Net (charge-offs) recoveries	549	12,636	(8,108)	8,382
Ending balance	327,132	355,003	327,132	355,003
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	61,011	76,123	69,125	65,405
Provision for credit losses	(309)	741	(5,132)	16,469
Net charge-offs
Charge-offs	(2,721)	(3,338)	(9,356)	(11,658)
Recoveries	1,511	1,655	4,855	4,965
Net (charge-offs) recoveries	(1,210)	(1,683)	(4,501)	(6,693)
Ending balance	59,492	75,181	59,492	75,181
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	211,220	182,987	200,564	170,809
Provision for credit losses	37,735	32,887	92,212	93,502
Net charge-offs
Charge-offs	(40,735)	(34,995)	(113,050)	(105,479)
Recoveries	13,914	12,951	42,408	34,998
Net (charge-offs) recoveries	(26,821)	(22,044)	(70,642)	(70,481)
Ending balance	222,134	193,830	222,134	193,830
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,485	77,547	78,045	78,300
Provision for credit losses	(251)	738	189	(15)
Net charge-offs
Ending balance	$ 78,234	$ 78,285	$ 78,234	$ 78,285