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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,248	$ 1,008,225	$ 1,017,198	$ 988,997
Provision for credit losses	16,000	30,000	94,000	137,000
Net charge-offs
Charge-offs	(52,066)	(47,052)	(166,265)	(171,298)
Recoveries	36,306	22,153	74,555	58,627
Net (charge-offs) recoveries	(15,760)	(24,899)	(91,710)	(112,671)
Ending balance	1,019,488	1,013,326	1,019,488	1,013,326
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,830	339,314	328,599	330,833
Provision for credit losses	(6,972)	2,451	11,508	44,642
Net charge-offs
Charge-offs	(11,792)	(9,714)	(41,273)	(51,318)
Recoveries	7,123	4,423	18,355	12,317
Net (charge-offs) recoveries	(4,669)	(5,291)	(22,918)	(39,001)
Ending balance	317,189	336,474	317,189	336,474
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	353,761	366,229	374,085	362,719
Provision for credit losses	(11,394)	(7,699)	(27,464)	1,201
Net charge-offs
Charge-offs	(1,941)	(258)	(7,855)	(7,556)
Recoveries	14,577	5,895	16,237	7,803
Net (charge-offs) recoveries	12,636	5,637	8,382	247
Ending balance	355,003	364,167	355,003	364,167
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	76,123	66,006	65,405	61,127
Provision for credit losses	741	1,267	16,469	14,067
Net charge-offs
Charge-offs	(3,338)	(4,206)	(11,658)	(16,364)
Recoveries	1,655	2,028	4,965	6,265
Net (charge-offs) recoveries	(1,683)	(2,178)	(6,693)	(10,099)
Ending balance	75,181	65,095	75,181	65,095
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	182,987	158,559	170,809	156,288
Provision for credit losses	32,887	33,886	93,502	76,908
Net charge-offs
Charge-offs	(34,995)	(32,874)	(105,479)	(96,060)
Recoveries	12,951	9,807	34,998	32,242
Net (charge-offs) recoveries	(22,044)	(23,067)	(70,481)	(63,818)
Ending balance	193,830	169,378	193,830	169,378
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	77,547	78,117	78,300	78,030
Provision for credit losses	738	95	(15)	182
Net charge-offs
Ending balance	$ 78,285	$ 78,212	$ 78,285	$ 78,212