Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 85,191,592	$ 85,325,604
30-89 Days Past Due	991,812	1,078,943
Accruing Loans Past Due 90 Days or More	235,325	244,405
Purchased Impaired	378,000	410,015
Nonaccrual	864,671	882,598
Loans and leases, net of unearned discount	87,710,749	87,988,983
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	49,349	47,418
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,377,917	21,332,234
30-89 Days Past Due	51,438	167,756
Accruing Loans Past Due 90 Days or More	5,547	1,322
Purchased Impaired	2	21
Nonaccrual	262,592	240,991
Loans and leases, net of unearned discount	21,697,522	21,742,651
Commercial, Financial, Leasing, etc. [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	26	327
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,919,508	24,910,381
30-89 Days Past Due	250,993	166,305
Accruing Loans Past Due 90 Days or More	3,311	4,444
Purchased Impaired	11,744	16,815
Nonaccrual	152,832	184,982
Loans and leases, net of unearned discount	25,342,957	25,288,943
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	4,569	6,016
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,641,644	1,618,973
30-89 Days Past Due	1,974	5,159
Purchased Impaired	357	1,135
Nonaccrual	4,519	6,451
Loans and leases, net of unearned discount	1,648,494	1,631,718
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,680,584	6,407,451
30-89 Days Past Due	71,115	23,467
Purchased Impaired	1,194	4,706
Nonaccrual	9,162	10,088
Loans and leases, net of unearned discount	6,762,055	6,445,712
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	14,942,659	15,376,759
30-89 Days Past Due	407,773	474,372
Accruing Loans Past Due 90 Days or More	221,666	233,437
Purchased Impaired	263,939	282,102
Nonaccrual	234,309	235,834
Loans and leases, net of unearned discount	16,078,762	16,610,086
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	8,416	7,582
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,599,705	2,718,019
30-89 Days Past Due	82,738	83,898
Purchased Impaired	100,764	105,236
Nonaccrual	98,977	96,105
Loans and leases, net of unearned discount	2,882,184	3,003,258
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,037,213	5,171,345
30-89 Days Past Due	32,100	38,546
Nonaccrual	73,169	74,500
Loans and leases, net of unearned discount	5,150,639	5,293,782
Home Equity Lines and Loans [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	8,157	9,391
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,468,893	3,441,371
30-89 Days Past Due	64,995	78,511
Nonaccrual	20,613	23,781
Loans and leases, net of unearned discount	3,554,501	3,543,663
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,523,469	4,349,071
30-89 Days Past Due	28,686	40,929
Accruing Loans Past Due 90 Days or More	4,801	5,202
Nonaccrual	8,498	9,866
Loans and leases, net of unearned discount	4,593,635	4,429,170
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 28,181	$ 24,102