Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,001,430	$ 962,752	$ 988,997	$ 955,992
Provision for credit losses	52,000	32,000	107,000	81,000
Net charge-offs
Charge-offs	(61,682)	(46,870)	(124,246)	(105,582)
Recoveries	16,477	22,614	36,474	39,086
Net (charge-offs) recoveries	(45,205)	(24,256)	(87,772)	(66,496)
Ending balance	1,008,225	970,496	1,008,225	970,496
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	347,760	323,866	330,833	300,404
Provision for credit losses	13,368	(10,919)	42,191	13,445
Net charge-offs
Charge-offs	(25,247)	(7,487)	(41,604)	(13,636)
Recoveries	3,433	10,619	7,894	15,866
Net (charge-offs) recoveries	(21,814)	3,132	(33,710)	2,230
Ending balance	339,314	316,079	339,314	316,079
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	360,010	331,985	362,719	326,831
Provision for credit losses	7,638	15,823	8,900	19,836
Net charge-offs
Charge-offs	(1,853)	(733)	(7,298)	(2,005)
Recoveries	434	2,599	1,908	5,012
Net (charge-offs) recoveries	(1,419)	1,866	(5,390)	3,007
Ending balance	366,229	349,674	366,229	349,674
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	62,012	68,371	61,127	72,238
Provision for credit losses	7,163	4,404	12,800	5,622
Net charge-offs
Charge-offs	(5,899)	(5,090)	(12,158)	(12,062)
Recoveries	2,730	1,975	4,237	3,862
Net (charge-offs) recoveries	(3,169)	(3,115)	(7,921)	(8,200)
Ending balance	66,006	69,660	66,006	69,660
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	153,172	160,819	156,288	178,320
Provision for credit losses	24,190	22,681	43,022	42,574
Net charge-offs
Charge-offs	(28,683)	(33,560)	(63,186)	(77,879)
Recoveries	9,880	7,421	22,435	14,346
Net (charge-offs) recoveries	(18,803)	(26,139)	(40,751)	(63,533)
Ending balance	158,559	157,361	158,559	157,361
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,476	77,711	78,030	78,199
Provision for credit losses	(359)	11	87	(477)
Net charge-offs
Ending balance	$ 78,117	$ 77,722	$ 78,117	$ 77,722