Loans and Leases and the Allowance for Credit Losses - Summary of Loan Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 68,540,248	$ 66,668,956
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,233,177	19,461,292
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	19,223,102	18,695,440
Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	785,660	588,407
Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	224,415	177,445
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	23,551,595	22,556,939
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,479,501	21,837,022
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	895,603	578,317
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	176,491	141,600
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,614,222	1,465,140
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,507,057	1,347,778
Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	61,143	45,845
Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	46,022	71,517
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3,554,720	3,545,490
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3,447,841	3,347,522
Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	94,567	172,269
Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 12,312	$ 25,699