Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 988,997	$ 955,992
Provision for credit losses	55,000	49,000
Net charge-offs
Charge-offs	(62,564)	(58,712)
Recoveries	19,997	16,472
Net (charge-offs) recoveries	(42,567)	(42,240)
Ending balance	1,001,430	962,752
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	330,833	300,404
Provision for credit losses	28,823	24,364
Net charge-offs
Charge-offs	(16,357)	(6,149)
Recoveries	4,461	5,247
Net (charge-offs) recoveries	(11,896)	(902)
Ending balance	347,760	323,866
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	362,719	326,831
Provision for credit losses	1,262	4,013
Net charge-offs
Charge-offs	(5,445)	(1,272)
Recoveries	1,474	2,413
Net (charge-offs) recoveries	(3,971)	1,141
Ending balance	360,010	331,985
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	61,127	72,238
Provision for credit losses	5,637	1,218
Net charge-offs
Charge-offs	(6,259)	(6,972)
Recoveries	1,507	1,887
Net (charge-offs) recoveries	(4,752)	(5,085)
Ending balance	62,012	68,371
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	156,288	178,320
Provision for credit losses	18,832	19,893
Net charge-offs
Charge-offs	(34,503)	(44,319)
Recoveries	12,555	6,925
Net (charge-offs) recoveries	(21,948)	(37,394)
Ending balance	153,172	160,819
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,030	78,199
Provision for credit losses	446	(488)
Net charge-offs
Ending balance	$ 78,476	$ 77,711