Loans and Leases - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 95,120,921	$ 87,999,720
30-89 Days Past Due	662,439	1,174,132
Accruing Loans Past Due 90 Days or More	859,208	518,728
Purchased Impaired		227,545
Nonaccrual	1,893,299	963,112
Loans and leases, net of unearned discount	98,535,867	90,922,869
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More		39,632
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	27,196,862	23,290,797
30-89 Days Past Due	60,822	184,011
Accruing Loans Past Due 90 Days or More	10,053	16,776
Nonaccrual	306,827	346,557
Loans and leases, net of unearned discount	27,574,564	23,838,168
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		27
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	26,688,515	26,311,414
30-89 Days Past Due	168,917	165,579
Accruing Loans Past Due 90 Days or More	47,014	6,740
Purchased Impaired		15,601
Nonaccrual	775,894	158,474
Loans and leases, net of unearned discount	27,680,340	26,657,808
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,246,095	1,521,315
30-89 Days Past Due	1,693	21,195
Accruing Loans Past Due 90 Days or More	856
Purchased Impaired		753
Nonaccrual	1,094	3,982
Loans and leases, net of unearned discount	1,249,738	1,547,245
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	8,523,591	7,204,148
30-89 Days Past Due	66,365	95,346
Accruing Loans Past Due 90 Days or More	3,816	3,360
Purchased Impaired		1,237
Nonaccrual	114,039	32,770
Loans and leases, net of unearned discount	8,707,811	7,336,861
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,764,836	12,760,040
30-89 Days Past Due	200,406	451,274
Accruing Loans Past Due 90 Days or More	792,888	486,515
Purchased Impaired		143,145
Nonaccrual	365,729	235,663
Loans and leases, net of unearned discount	15,123,859	14,082,425
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More		5,788
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,462,277	1,858,037
30-89 Days Past Due	19,687	65,215
Accruing Loans Past Due 90 Days or More		181
Purchased Impaired		66,809
Nonaccrual	147,170	83,427
Loans and leases, net of unearned discount	1,629,134	2,073,669
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,881,885	4,386,511
30-89 Days Past Due	24,329	30,229
Nonaccrual	79,392	63,215
Loans and leases, net of unearned discount	3,985,606	4,481,617
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		1,662
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,002,643	5,484,997
30-89 Days Past Due	47,161	36,827
Nonaccrual	25,519	14,219
Loans and leases, net of unearned discount	7,075,323	5,536,142
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		99
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,007,349	3,787,221
30-89 Days Past Due	55,498	78,478
Nonaccrual	39,404	21,293
Loans and leases, net of unearned discount	4,102,251	3,886,992
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,346,868	1,395,240
30-89 Days Past Due	17,561	45,978
Accruing Loans Past Due 90 Days or More	4,581	5,156
Nonaccrual	38,231	3,512
Loans and leases, net of unearned discount	$ 1,407,241	1,481,942
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More		$ 32,056