Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 95,806,020	$ 87,999,720
30-89 Days Past Due	873,798	1,174,132
Accruing Loans Past Due 90 Days or More	527,258	518,728
Nonaccrual	1,239,972	963,112
Loans and leases, net of unearned discount	98,447,048	90,922,869
Purchased Impaired		227,545
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	27,249,552	23,290,797
30-89 Days Past Due	282,917	184,011
Accruing Loans Past Due 90 Days or More	8,551	16,776
Nonaccrual	350,628	346,557
Loans and leases, net of unearned discount	27,891,648	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	27,250,676	26,311,414
30-89 Days Past Due	197,881	165,579
Accruing Loans Past Due 90 Days or More	8,189	6,740
Nonaccrual	252,515	158,474
Loans and leases, net of unearned discount	27,709,261	26,657,808
Purchased Impaired		15,601
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,353,863	1,521,315
30-89 Days Past Due	7,282	21,195
Nonaccrual	1,833	3,982
Loans and leases, net of unearned discount	1,362,978	1,547,245
Purchased Impaired		753
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	8,405,525	7,204,148
30-89 Days Past Due	66,599	95,346
Accruing Loans Past Due 90 Days or More	94	3,360
Nonaccrual	37,627	32,770
Loans and leases, net of unearned discount	8,509,845	7,336,861
Purchased Impaired		1,237
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,934,309	12,760,040
30-89 Days Past Due	185,420	451,274
Accruing Loans Past Due 90 Days or More	503,450	486,515
Nonaccrual	297,636	235,663
Loans and leases, net of unearned discount	14,920,815	14,082,425
Purchased Impaired		143,145
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	1,606,130	1,858,037
30-89 Days Past Due	20,980	65,215
Accruing Loans Past Due 90 Days or More		181
Nonaccrual	115,783	83,427
Loans and leases, net of unearned discount	1,742,893	2,073,669
Purchased Impaired		66,809
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,000,829	4,386,511
30-89 Days Past Due	22,209	30,229
Nonaccrual	78,820	63,215
Loans and leases, net of unearned discount	4,101,858	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	6,838,126	5,484,997
30-89 Days Past Due	36,003	36,827
Nonaccrual	24,191	14,219
Loans and leases, net of unearned discount	6,898,320	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	3,829,968	3,787,221
30-89 Days Past Due	42,906	78,478
Nonaccrual	42,374	21,293
Loans and leases, net of unearned discount	3,915,248	3,886,992
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,337,042	1,395,240
30-89 Days Past Due	11,601	45,978
Accruing Loans Past Due 90 Days or More	6,974	5,156
Nonaccrual	38,565	3,512
Loans and leases, net of unearned discount	$ 1,394,182	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