Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 955,992	$ 919,562
Provision for credit losses	49,000	38,000
Net charge-offs
Charge-offs	(58,712)	(47,476)
Recoveries	16,472	11,287
Net charge-offs	(42,240)	(36,189)
Ending balance	962,752	921,373
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	300,404	288,038
Provision for credit losses	24,364	1,442
Net charge-offs
Charge-offs	(6,149)	(12,350)
Recoveries	5,247	3,939
Net charge-offs	(902)	(8,411)
Ending balance	323,866	281,069
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	326,831	307,927
Provision for credit losses	4,013	15,542
Net charge-offs
Charge-offs	(1,272)	(6,679)
Recoveries	2,413	585
Net charge-offs	1,141	(6,094)
Ending balance	331,985	317,375
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	72,238	61,910
Provision for credit losses	1,218	960
Net charge-offs
Charge-offs	(6,972)	(3,118)
Recoveries	1,887	989
Net charge-offs	(5,085)	(2,129)
Ending balance	68,371	60,741
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	178,320	186,033
Provision for credit losses	19,893	19,574
Net charge-offs
Charge-offs	(44,319)	(25,329)
Recoveries	6,925	5,774
Net charge-offs	(37,394)	(19,555)
Ending balance	160,819	186,052
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,199	75,654
Provision for credit losses	(488)	482
Net charge-offs
Ending balance	$ 77,711	$ 76,136