Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 955,992	$ 919,562	$ 916,676
Provision for credit losses	190,000	170,000	124,000
Net charge-offs
Charge-offs	(231,255)	(198,373)	(178,742)
Recoveries	74,260	64,803	57,628
Net (charge-offs) recoveries	(156,995)	(133,570)	(121,114)
Ending balance	988,997	955,992	919,562
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	300,404	288,038	273,383
Provision for credit losses	59,506	43,065	51,410
Net charge-offs
Charge-offs	(59,244)	(60,983)	(58,943)
Recoveries	30,167	30,284	22,188
Net (charge-offs) recoveries	(29,077)	(30,699)	(36,755)
Ending balance	330,833	300,404	288,038
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	326,831	307,927	324,978
Provision for credit losses	33,627	25,768	(13,779)
Net charge-offs
Charge-offs	(4,805)	(16,487)	(14,058)
Recoveries	7,066	9,623	10,786
Net (charge-offs) recoveries	2,261	(6,864)	(3,272)
Ending balance	362,719	326,831	307,927
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	72,238	61,910	78,656
Provision for credit losses	6,902	19,133	(3,974)
Net charge-offs
Charge-offs	(26,133)	(13,116)	(21,351)
Recoveries	8,120	4,311	8,579
Net (charge-offs) recoveries	(18,013)	(8,805)	(12,772)
Ending balance	61,127	72,238	61,910
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	178,320	186,033	164,644
Provision for credit losses	90,134	79,489	89,704
Net charge-offs
Charge-offs	(141,073)	(107,787)	(84,390)
Recoveries	28,907	20,585	16,075
Net (charge-offs) recoveries	(112,166)	(87,202)	(68,315)
Ending balance	156,288	178,320	186,033
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,199	75,654	75,015
Provision for credit losses	(169)	2,545	639
Net charge-offs
Ending balance	$ 78,030	$ 78,199	$ 75,654