Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 929,987	$ 917,666	$ 919,562	$ 916,676
Provision for credit losses	44,000	29,000	112,000	91,000
Net charge-offs
Charge-offs	(53,141)	(43,092)	(133,579)	(132,369)
Recoveries	12,952	15,059	35,815	43,326
Net charge-offs	(40,189)	(28,033)	(97,764)	(89,043)
Ending balance	933,798	918,633	933,798	918,633
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	286,750	292,251	288,038	273,383
Provision for credit losses	21,507	2,373	32,686	40,527
Net charge-offs
Charge-offs	(26,912)	(15,921)	(46,990)	(44,872)
Recoveries	5,322	7,849	12,933	17,514
Net charge-offs	(21,590)	(8,072)	(34,057)	(27,358)
Ending balance	286,667	286,552	286,667	286,552
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	311,294	311,254	307,927	324,978
Provision for credit losses	1,879	8,046	13,769	(4,067)
Net charge-offs
Charge-offs	(2,203)	(1,666)	(12,352)	(7,966)
Recoveries	2,119	1,267	3,745	5,956
Net charge-offs	(84)	(399)	(8,607)	(2,010)
Ending balance	313,089	318,901	313,089	318,901
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	60,294	72,404	61,910	78,656
Provision for credit losses	(3,155)	(3,187)	(571)	(916)
Net charge-offs
Charge-offs	(3,268)	(4,193)	(9,695)	(17,124)
Recoveries	1,125	2,498	3,352	6,906
Net charge-offs	(2,143)	(1,695)	(6,343)	(10,218)
Ending balance	54,996	67,522	54,996	67,522
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	194,238	165,871	186,033	164,644
Provision for credit losses	24,448	21,815	65,038	54,632
Net charge-offs
Charge-offs	(20,758)	(21,312)	(64,542)	(62,407)
Recoveries	4,386	3,445	15,785	12,950
Net charge-offs	(16,372)	(17,867)	(48,757)	(49,457)
Ending balance	202,314	169,819	202,314	169,819
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	77,411	75,886	75,654	75,015
Provision for credit losses	(679)	(47)	1,078	824
Net charge-offs
Ending balance	$ 76,732	$ 75,839	$ 76,732	$ 75,839