Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 85,328,234	$ 85,325,604
30-89 Days Past Due	1,026,336	1,078,943
Accruing Loans Past Due 90 Days or More	223,026	244,405
Purchased Impaired	352,465	410,015
Nonaccrual	819,984	882,598
Loans and leases, net of unearned discount	87,797,450	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	47,405	47,418
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,615,676	21,332,234
30-89 Days Past Due	29,906	167,756
Accruing Loans Past Due 90 Days or More	4,210	1,322
Purchased Impaired	3	21
Nonaccrual	245,031	240,991
Loans and leases, net of unearned discount	21,894,857	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	31	327
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,352,075	24,910,381
30-89 Days Past Due	212,480	166,305
Accruing Loans Past Due 90 Days or More	10,621	4,444
Purchased Impaired	10,579	16,815
Nonaccrual	153,552	184,982
Loans and leases, net of unearned discount	25,743,637	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	4,330	6,016
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,628,793	1,618,973
30-89 Days Past Due	8,668	5,159
Purchased Impaired	547	1,135
Nonaccrual	5,212	6,451
Loans and leases, net of unearned discount	1,643,220	1,631,718
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,597,814	6,407,451
30-89 Days Past Due	140,490	23,467
Accruing Loans Past Due 90 Days or More	4,000
Purchased Impaired	1,053	4,706
Nonaccrual	7,723	10,088
Loans and leases, net of unearned discount	6,751,080	6,445,712
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	14,456,180	15,376,759
30-89 Days Past Due	425,894	474,372
Accruing Loans Past Due 90 Days or More	200,159	233,437
Purchased Impaired	244,865	282,102
Nonaccrual	215,850	235,834
Loans and leases, net of unearned discount	15,550,967	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	8,019	7,582
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,488,340	2,718,019
30-89 Days Past Due	79,179	83,898
Purchased Impaired	95,418	105,236
Nonaccrual	96,808	96,105
Loans and leases, net of unearned discount	2,759,745	3,003,258
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,931,331	5,171,345
30-89 Days Past Due	29,589	38,546
Accruing Loans Past Due 90 Days or More	49
Nonaccrual	66,690	74,500
Loans and leases, net of unearned discount	5,034,515	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	6,856	9,391
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,450,113	3,441,371
30-89 Days Past Due	69,398	78,511
Nonaccrual	19,564	23,781
Loans and leases, net of unearned discount	3,539,075	3,543,663
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,807,912	4,349,071
30-89 Days Past Due	30,732	40,929
Accruing Loans Past Due 90 Days or More	3,987	5,202
Nonaccrual	9,554	9,866
Loans and leases, net of unearned discount	4,880,354	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	$ 28,169	$ 24,102