Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 95,564,931	$ 95,120,921
30-89 Days Past Due	692,490	662,439
Accruing Loans Past Due 90 Days or More	1,084,553	859,208
Nonaccrual	1,957,106	1,893,299
Loans and leases, net of unearned discount	99,299,080	98,535,867
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	27,327,644	27,196,862
30-89 Days Past Due	182,686	60,822
Accruing Loans Past Due 90 Days or More	5,791	10,053
Nonaccrual	295,069	306,827
Loans and leases, net of unearned discount	27,811,190	27,574,564
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	26,369,232	26,688,515
30-89 Days Past Due	175,904	168,917
Accruing Loans Past Due 90 Days or More	26,996	47,014
Nonaccrual	824,079	775,894
Loans and leases, net of unearned discount	27,396,211	27,680,340
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,269,858	1,246,095
30-89 Days Past Due	7,909	1,693
Accruing Loans Past Due 90 Days or More		856
Nonaccrual	1,224	1,094
Loans and leases, net of unearned discount	1,278,991	1,249,738
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	8,580,462	8,523,591
30-89 Days Past Due	37,986	66,365
Accruing Loans Past Due 90 Days or More	6,099	3,816
Nonaccrual	126,225	114,039
Loans and leases, net of unearned discount	8,750,772	8,707,811
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	14,198,898	13,764,836
30-89 Days Past Due	191,860	200,406
Accruing Loans Past Due 90 Days or More	1,041,873	792,888
Nonaccrual	385,508	365,729
Loans and leases, net of unearned discount	15,818,139	15,123,859
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,372,339	1,462,277
30-89 Days Past Due	16,136	19,687
Nonaccrual	143,069	147,170
Loans and leases, net of unearned discount	1,531,544	1,629,134
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,720,689	3,881,885
30-89 Days Past Due	15,926	24,329
Nonaccrual	79,188	79,392
Loans and leases, net of unearned discount	3,815,803	3,985,606
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,228,228	7,002,643
30-89 Days Past Due	26,821	47,161
Nonaccrual	27,218	25,519
Loans and leases, net of unearned discount	7,282,267	7,075,323
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,178,258	4,007,349
30-89 Days Past Due	28,970	55,498
Nonaccrual	38,219	39,404
Loans and leases, net of unearned discount	4,245,447	4,102,251
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,319,323	1,346,868
30-89 Days Past Due	8,292	17,561
Accruing Loans Past Due 90 Days or More	3,794	4,581
Nonaccrual	37,307	38,231
Loans and leases, net of unearned discount	$ 1,368,716	$ 1,407,241