Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 919,562	$ 916,676	$ 925,860
Provision for credit losses	170,000	124,000	185,000
Allowance related to loans sold or securitized			(11,000)
Net charge-offs
Charge-offs	(198,373)	(178,742)	(253,510)
Recoveries	64,803	57,628	70,326
Net charge-offs	(133,570)	(121,114)	(183,184)
Ending balance	955,992	919,562	916,676
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	288,038	273,383	246,759
Provision for credit losses	43,065	51,410	124,180
Net charge-offs
Charge-offs	(60,983)	(58,943)	(109,329)
Recoveries	30,284	22,188	11,773
Net charge-offs	(30,699)	(36,755)	(97,556)
Ending balance	300,404	288,038	273,383
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	307,927	324,978	337,101
Provision for credit losses	25,768	(13,779)	275
Net charge-offs
Charge-offs	(16,487)	(14,058)	(34,595)
Recoveries	9,623	10,786	22,197
Net charge-offs	(6,864)	(3,272)	(12,398)
Ending balance	326,831	307,927	324,978
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	61,910	78,656	88,807
Provision for credit losses	19,133	(3,974)	3,149
Net charge-offs
Charge-offs	(13,116)	(21,351)	(23,621)
Recoveries	4,311	8,579	10,321
Net charge-offs	(8,805)	(12,772)	(13,300)
Ending balance	72,238	61,910	78,656
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	186,033	164,644	179,418
Provision for credit losses	79,489	89,704	56,156
Allowance related to loans sold or securitized			(11,000)
Net charge-offs
Charge-offs	(107,787)	(84,390)	(85,965)
Recoveries	20,585	16,075	26,035
Net charge-offs	(87,202)	(68,315)	(59,930)
Ending balance	178,320	186,033	164,644
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	75,654	75,015	73,775
Provision for credit losses	2,545	639	1,240
Net charge-offs
Ending balance	$ 78,199	$ 75,654	$ 75,015