Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 84,280,045	$ 85,325,604
30-89 Days Past Due	905,045	1,078,943
Accruing Loans Past Due 90 Days or More	254,360	244,405
Purchased Impaired	325,980	410,015
Nonaccrual	870,832	882,598
Loans and leases, net of unearned discount	86,680,485	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	44,223	47,418
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,317,925	21,332,234
30-89 Days Past Due	81,323	167,756
Accruing Loans Past Due 90 Days or More	1,390	1,322
Purchased Impaired		21
Nonaccrual	234,656	240,991
Loans and leases, net of unearned discount	21,635,394	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	100	327
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,650,660	24,910,381
30-89 Days Past Due	97,630	166,305
Accruing Loans Past Due 90 Days or More	52,436	4,444
Purchased Impaired	9,948	16,815
Nonaccrual	207,584	184,982
Loans and leases, net of unearned discount	25,022,535	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	4,277	6,016
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,631,501	1,618,973
30-89 Days Past Due	7,354	5,159
Accruing Loans Past Due 90 Days or More	1,656
Purchased Impaired		1,135
Nonaccrual	2,786	6,451
Loans and leases, net of unearned discount	1,643,411	1,631,718
Residential Builder and Developer [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	114
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,792,917	6,407,451
30-89 Days Past Due	39,598	23,467
Accruing Loans Past Due 90 Days or More	440
Purchased Impaired	571	4,706
Nonaccrual	18,887	10,088
Loans and leases, net of unearned discount	6,852,429	6,445,712
Other Commercial Construction [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	16
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,989,937	15,376,759
30-89 Days Past Due	437,170	474,372
Accruing Loans Past Due 90 Days or More	193,604	233,437
Purchased Impaired	224,618	282,102
Nonaccrual	227,619	235,834
Loans and leases, net of unearned discount	15,080,013	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	7,065	7,582
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,373,778	2,718,019
30-89 Days Past Due	93,582	83,898
Accruing Loans Past Due 90 Days or More	729
Purchased Impaired	90,843	105,236
Nonaccrual	82,454	96,105
Loans and leases, net of unearned discount	2,641,386	3,003,258
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,850,989	5,171,345
30-89 Days Past Due	35,212	38,546
Nonaccrual	66,303	74,500
Loans and leases, net of unearned discount	4,957,198	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	4,694	9,391
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,527,867	3,441,371
30-89 Days Past Due	71,184	78,511
Nonaccrual	20,949	23,781
Loans and leases, net of unearned discount	3,620,000	3,543,663
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,144,471	4,349,071
30-89 Days Past Due	41,992	40,929
Accruing Loans Past Due 90 Days or More	4,105	5,202
Nonaccrual	9,594	9,866
Loans and leases, net of unearned discount	5,228,119	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	$ 27,957	$ 24,102