Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 86,248,711	$ 86,140,950
30-89 Days Past Due	942,526	866,337
Accruing Loans Past Due 90 Days or More	244,257	222,527
Purchased Impaired	278,783	303,305
Nonaccrual	881,611	893,608
Loans and leases, net of unearned discount	88,639,883	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	43,995	39,750
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	22,701,500	22,701,020
30-89 Days Past Due	141,555	39,798
Accruing Loans Past Due 90 Days or More	1,047	2,567
Nonaccrual	245,819	234,423
Loans and leases, net of unearned discount	23,090,204	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	283	168
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,441,419	25,250,983
30-89 Days Past Due	159,209	134,474
Accruing Loans Past Due 90 Days or More	7,394	11,457
Purchased Impaired	10,305	9,769
Nonaccrual	207,709	203,672
Loans and leases, net of unearned discount	25,826,194	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	158	10
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,738,846	1,665,178
30-89 Days Past Due	2,190	20,333
Purchased Impaired	549
Nonaccrual	4,392	4,798
Loans and leases, net of unearned discount	1,745,977	1,690,309
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,036,036	6,982,077
30-89 Days Past Due	31,152	43,615
Accruing Loans Past Due 90 Days or More	31,032	14,344
Purchased Impaired	640	641
Nonaccrual	19,899	22,205
Loans and leases, net of unearned discount	7,118,759	7,062,882
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,337,558	13,591,790
30-89 Days Past Due	406,106	404,808
Accruing Loans Past Due 90 Days or More	199,940	189,682
Purchased Impaired	187,631	203,044
Nonaccrual	210,266	233,352
Loans and leases, net of unearned discount	14,347,926	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	6,425	6,650
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,186,132	2,278,040
30-89 Days Past Due	71,354	72,544
Purchased Impaired	79,658	89,851
Nonaccrual	84,863	84,685
Loans and leases, net of unearned discount	2,422,007	2,525,120
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,634,634	4,758,513
30-89 Days Past Due	31,145	25,416
Nonaccrual	69,245	71,292
Loans and leases, net of unearned discount	4,739,895	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	4,871	5,033
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,295,732	4,085,781
30-89 Days Past Due	22,549	29,947
Nonaccrual	10,972	11,199
Loans and leases, net of unearned discount	4,329,488	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	235	235
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,619,015	3,555,757
30-89 Days Past Due	62,846	79,804
Nonaccrual	21,209	23,359
Loans and leases, net of unearned discount	3,703,070	3,658,920
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,257,839	1,271,811
30-89 Days Past Due	14,420	15,598
Accruing Loans Past Due 90 Days or More	4,844	4,477
Nonaccrual	7,237	4,623
Loans and leases, net of unearned discount	1,316,363	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	$ 32,023	$ 27,654