Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 65,332,727	$ 64,785,780
30-89 Days past due	474,980	530,901
Purchased impaired	184,018	197,737
Nonaccrual	790,586	799,151
Loans and leases, net of unearned discount	67,099,042	66,668,956
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	19,519,566	19,228,265
30-89 Days past due	43,213	37,246
Purchased impaired	9,724	10,300
Nonaccrual	195,403	177,445
Loans and leases, net of unearned discount	19,775,494	19,461,292
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	22,225,088	22,208,491
30-89 Days past due	116,465	118,704
Purchased impaired	45,752	51,312
Nonaccrual	142,007	141,600
Loans and leases, net of unearned discount	22,573,760	22,556,939
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,460,981	1,273,607
30-89 Days past due	6,119	11,827
Purchased impaired	91,839	98,347
Nonaccrual	65,310	71,517
Loans and leases, net of unearned discount	1,631,202	1,465,140
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,575,578	3,484,932
30-89 Days past due	18,244	17,678
Purchased impaired	17,061	17,181
Nonaccrual	24,280	25,699
Loans and leases, net of unearned discount	3,640,748	3,545,490
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,580,514	7,640,368
30-89 Days past due	189,901	226,932
Purchased impaired	17,283	18,223
Nonaccrual	171,496	180,275
Loans and leases, net of unearned discount	8,176,551	8,318,013
Residential Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	241,467	249,810
30-89 Days past due	11,831	11,774
Nonaccrual	74,270	77,704
Loans and leases, net of unearned discount	327,568	339,288
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,783,865	5,859,378
30-89 Days past due	35,478	42,945
Purchased impaired	2,359	2,374
Nonaccrual	87,985	89,291
Loans and leases, net of unearned discount	5,922,985	6,021,884
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,024,526	1,931,138
30-89 Days past due	25,322	30,500
Nonaccrual	14,100	17,578
Loans and leases, net of unearned discount	2,063,948	1,979,349
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,921,142	2,909,791
30-89 Days past due	28,407	33,295
Nonaccrual	15,735	18,042
Loans and leases, net of unearned discount	2,986,786	2,981,561
Non-Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	236,621	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	4,265	1,805
Non-Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	27,261	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	3,864
Non-Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	197,299	216,489
Non-Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	3,932	4,064
Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	80,110	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	3,323	6,231
Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	17,187	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	6,953	9,350
Acquired [Member] | Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	1,721
Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	20,058	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	13,298	27,896
Acquired [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing		133
Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	$ 17,570	$ 16,369