Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 919,562	$ 916,676
Provision for credit losses	38,000	32,000
Net charge-offs
Charge-offs	(47,476)	(47,439)
Recoveries	11,287	15,531
Net charge-offs	(36,189)	(31,908)
Ending balance	921,373	916,768
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	288,038	273,383
Provision for credit losses	1,442	12,598
Net charge-offs
Charge-offs	(12,350)	(14,809)
Recoveries	3,939	5,663
Net charge-offs	(8,411)	(9,146)
Ending balance	281,069	276,835
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	307,927	324,978
Provision for credit losses	15,542	116
Net charge-offs
Charge-offs	(6,679)	(3,486)
Recoveries	585	3,197
Net charge-offs	(6,094)	(289)
Ending balance	317,375	324,805
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	61,910	78,656
Provision for credit losses	960	4,228
Net charge-offs
Charge-offs	(3,118)	(7,453)
Recoveries	989	1,631
Net charge-offs	(2,129)	(5,822)
Ending balance	60,741	77,062
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	186,033	164,644
Provision for credit losses	19,574	14,141
Net charge-offs
Charge-offs	(25,329)	(21,691)
Recoveries	5,774	5,040
Net charge-offs	(19,555)	(16,651)
Ending balance	186,052	162,134
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	75,654	75,015
Provision for credit losses	482	917
Net charge-offs
Ending balance	$ 76,136	$ 75,932