Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 87,441,215	$ 86,140,950
30-89 Days Past Due	916,630	866,337
Accruing Loans Past Due 90 Days or More	348,725	222,527
Purchased Impaired	263,025	303,305
Nonaccrual	865,384	893,608
Loans and leases, net of unearned discount	89,878,058	88,466,477
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	43,079	39,750
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	23,177,367	22,701,020
30-89 Days Past Due	26,974	39,798
Accruing Loans Past Due 90 Days or More	3,332	2,567
Purchased Impaired	2
Nonaccrual	223,733	234,423
Loans and leases, net of unearned discount	23,431,408	22,977,976
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		168
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,829,322	25,250,983
30-89 Days Past Due	146,704	134,474
Accruing Loans Past Due 90 Days or More	12,450	11,457
Purchased Impaired	12,867	9,769
Nonaccrual	203,116	203,672
Loans and leases, net of unearned discount	26,204,849	25,610,365
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	390	10
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,665,951	1,665,178
30-89 Days Past Due	6,495	20,333
Purchased Impaired	468
Nonaccrual	5,985	4,798
Loans and leases, net of unearned discount	1,678,899	1,690,309
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,217,573	6,982,077
30-89 Days Past Due	55,060	43,615
Accruing Loans Past Due 90 Days or More	4,600	14,344
Purchased Impaired	625	641
Nonaccrual	32,769	22,205
Loans and leases, net of unearned discount	7,310,627	7,062,882
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,206,787	13,591,790
30-89 Days Past Due	462,391	404,808
Accruing Loans Past Due 90 Days or More	321,810	189,682
Purchased Impaired	172,718	203,044
Nonaccrual	210,922	233,352
Loans and leases, net of unearned discount	14,380,609	14,629,326
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	5,981	6,650
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,067,375	2,278,040
30-89 Days Past Due	81,857	72,544
Purchased Impaired	76,345	89,851
Nonaccrual	87,551	84,685
Loans and leases, net of unearned discount	2,313,128	2,525,120
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,562,840	4,758,513
30-89 Days Past Due	29,972	25,416
Nonaccrual	66,927	71,292
Loans and leases, net of unearned discount	4,664,099	4,860,254
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	4,360	5,033
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,759,183	4,085,781
30-89 Days Past Due	24,485	29,947
Nonaccrual	11,153	11,199
Loans and leases, net of unearned discount	4,795,116	4,127,162
Recreational Finance [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	295	235
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,639,155	3,555,757
30-89 Days Past Due	70,177	79,804
Nonaccrual	20,170	23,359
Loans and leases, net of unearned discount	3,729,502	3,658,920
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,315,662	1,271,811
30-89 Days Past Due	12,515	15,598
Accruing Loans Past Due 90 Days or More	6,533	4,477
Nonaccrual	3,058	4,623
Loans and leases, net of unearned discount	1,369,821	1,324,163
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 32,053	$ 27,654