Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	$ 836,574	$ 662,439
Accruing Loans Past Due 90 Days or More	1,026,080	859,208
Nonaccrual	2,242,263	1,893,299
Loans and leases, net of unearned discount	93,582,894	98,535,867
Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	89,477,977	95,120,921
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	121,993	60,822
Accruing Loans Past Due 90 Days or More	11,945	10,053
Nonaccrual	280,189	306,827
Loans and leases, net of unearned discount	22,514,940	27,574,564
Commercial, Financial, Leasing, etc. [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	22,100,813	27,196,862
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	245,157	168,917
Accruing Loans Past Due 90 Days or More	63,368	47,014
Nonaccrual	1,152,870	775,894
Loans and leases, net of unearned discount	26,985,800	27,680,340
Commercial [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,524,405	26,688,515
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	16,453	1,693
Accruing Loans Past Due 90 Days or More	2,392	856
Nonaccrual	594	1,094
Loans and leases, net of unearned discount	1,356,323	1,249,738
Residential Builder and Developer [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,336,884	1,246,095
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	93,978	66,365
Accruing Loans Past Due 90 Days or More	121	3,816
Nonaccrual	158,699	114,039
Loans and leases, net of unearned discount	8,681,829	8,707,811
Other Commercial Construction [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	8,429,031	8,523,591
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	255,187	200,406
Accruing Loans Past Due 90 Days or More	945,148	792,888
Nonaccrual	353,426	365,729
Loans and leases, net of unearned discount	14,867,963	15,123,859
Residential [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,314,202	13,764,836
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	15,690	19,687
Nonaccrual	126,529	147,170
Loans and leases, net of unearned discount	1,341,391	1,629,134
Residential Limited Documentation [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,199,172	1,462,277
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	14,712	24,329
Nonaccrual	71,474	79,392
Loans and leases, net of unearned discount	3,635,006	3,985,606
Home Equity Lines and Loans [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,548,820	3,881,885
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	29,656	47,161
Nonaccrual	23,907	25,519
Loans and leases, net of unearned discount	8,025,688	7,075,323
Recreational Finance [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,972,125	7,002,643
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	34,349	55,498
Nonaccrual	31,002	39,404
Loans and leases, net of unearned discount	4,618,657	4,102,251
Automobile [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,553,306	4,007,349
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	9,399	17,561
Accruing Loans Past Due 90 Days or More	3,106	4,581
Nonaccrual	43,573	38,231
Loans and leases, net of unearned discount	1,555,297	1,407,241
Other [Member] | Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 1,499,219	$ 1,346,868