Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,017,198	$ 988,997	$ 955,992
Provision for credit losses	132,000	168,000	190,000
Net charge-offs
Charge-offs	(231,241)	(224,598)	(231,255)
Recoveries	101,487	84,799	74,260
Net (charge-offs) recoveries	(129,754)	(139,799)	(156,995)
Ending balance	1,019,444	1,017,198	988,997
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,599	330,833	300,404
Provision for credit losses	33,967	41,511	59,506
Net charge-offs
Charge-offs	(60,414)	(64,941)	(59,244)
Recoveries	27,903	21,196	30,167
Net (charge-offs) recoveries	(32,511)	(43,745)	(29,077)
Ending balance	330,055	328,599	330,833
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	374,085	362,719	326,831
Provision for credit losses	(41,181)	6,715	33,627
Net charge-offs
Charge-offs	(12,286)	(7,931)	(4,805)
Recoveries	21,037	12,582	7,066
Net (charge-offs) recoveries	8,751	4,651	2,261
Ending balance	341,655	374,085	362,719
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	65,405	61,127	72,238
Provision for credit losses	12,401	16,094	6,902
Net charge-offs
Charge-offs	(15,345)	(20,799)	(26,133)
Recoveries	6,664	8,983	8,120
Net (charge-offs) recoveries	(8,681)	(11,816)	(18,013)
Ending balance	69,125	65,405	61,127
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	170,809	156,288	178,320
Provision for credit losses	127,068	103,410	90,134
Net charge-offs
Charge-offs	(143,196)	(130,927)	(141,073)
Recoveries	45,883	42,038	28,907
Net (charge-offs) recoveries	(97,313)	(88,889)	(112,166)
Ending balance	200,564	170,809	156,288
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,300	78,030	78,199
Provision for credit losses	(255)	270	(169)
Net charge-offs
Ending balance	$ 78,045	$ 78,300	$ 78,030