Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 66,788,173	$ 64,785,780
30-89 Days past due	503,264	530,901
Purchased impaired	149,421	197,737
Nonaccrual	787,098	799,151
Loans and leases, net of unearned discount	68,540,248	66,668,956
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	19,965,307	19,228,265
30-89 Days past due	29,451	37,246
Purchased impaired	4,645	10,300
Nonaccrual	224,415	177,445
Loans and leases, net of unearned discount	20,233,177	19,461,292
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	23,184,906	22,208,491
30-89 Days past due	105,140	118,704
Purchased impaired	45,523	51,312
Nonaccrual	176,491	141,600
Loans and leases, net of unearned discount	23,551,595	22,556,939
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,479,659	1,273,607
30-89 Days past due	15,951	11,827
Purchased impaired	65,102	98,347
Nonaccrual	46,022	71,517
Loans and leases, net of unearned discount	1,614,222	1,465,140
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,493,349	3,484,932
30-89 Days past due	28,433	17,678
Purchased impaired	17,484	17,181
Nonaccrual	12,312	25,699
Loans and leases, net of unearned discount	3,554,720	3,545,490
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,323,813	7,640,368
30-89 Days past due	206,044	226,932
Purchased impaired	14,392	18,223
Nonaccrual	153,354	180,275
Loans and leases, net of unearned discount	7,908,178	8,318,013
Residential Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	226,871	249,810
30-89 Days past due	11,662	11,774
Nonaccrual	64,351	77,704
Loans and leases, net of unearned discount	302,884	339,288
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,710,632	5,859,378
30-89 Days past due	38,506	42,945
Purchased impaired	2,275	2,374
Nonaccrual	78,126	89,291
Loans and leases, net of unearned discount	5,844,993	6,021,884
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,319,556	1,931,138
30-89 Days past due	36,867	30,500
Nonaccrual	13,892	17,578
Loans and leases, net of unearned discount	2,370,368	1,979,349
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,084,080	2,909,791
30-89 Days past due	31,210	33,295
Nonaccrual	18,135	18,042
Loans and leases, net of unearned discount	3,160,111	2,981,561
Non-Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	231,465	245,020
Non-Acquired [Member] | Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	5,882	1,805
Non-Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	21,629	22,170
Non-Acquired [Member] | Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing		492
Non-Acquired [Member] | Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	1,373
Non-Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	194,280	216,489
Non-Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	8,301	4,064
Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	80,827	110,367
Acquired [Member] | Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	3,477	6,231
Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	17,906	14,662
Acquired [Member] | Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	7,488	9,350
Acquired [Member] | Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	1,769
Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	16,295	35,726
Acquired [Member] | Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	15,454	27,896
Acquired [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	53	133
Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	$ 18,385	$ 16,369