Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 93,154,130	$ 95,120,921
30-89 Days Past Due	640,018	662,439
Accruing Loans Past Due 90 Days or More	1,077,227	859,208
Nonaccrual	2,242,057	1,893,299
Loans and leases, net of unearned discount	97,113,432	98,535,867
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,003,487	27,196,862
30-89 Days Past Due	70,202	60,822
Accruing Loans Past Due 90 Days or More	5,562	10,053
Nonaccrual	330,040	306,827
Loans and leases, net of unearned discount	25,409,291	27,574,564
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	26,112,046	26,688,515
30-89 Days Past Due	106,638	168,917
Accruing Loans Past Due 90 Days or More	36,780	47,014
Nonaccrual	1,081,546	775,894
Loans and leases, net of unearned discount	27,337,010	27,680,340
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,261,163	1,246,095
30-89 Days Past Due	13,773	1,693
Accruing Loans Past Due 90 Days or More	203	856
Nonaccrual	14,552	1,094
Loans and leases, net of unearned discount	1,289,691	1,249,738
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	8,627,896	8,523,591
30-89 Days Past Due	165,242	66,365
Accruing Loans Past Due 90 Days or More	5,178	3,816
Nonaccrual	133,758	114,039
Loans and leases, net of unearned discount	8,932,074	8,707,811
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,693,812	13,764,836
30-89 Days Past Due	185,110	200,406
Accruing Loans Past Due 90 Days or More	1,026,449	792,888
Nonaccrual	372,144	365,729
Loans and leases, net of unearned discount	15,277,515	15,123,859
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,277,064	1,462,277
30-89 Days Past Due	13,689	19,687
Nonaccrual	136,683	147,170
Loans and leases, net of unearned discount	1,427,436	1,629,134
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,612,791	3,881,885
30-89 Days Past Due	16,043	24,329
Nonaccrual	76,711	79,392
Loans and leases, net of unearned discount	3,705,545	3,985,606
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,707,774	7,002,643
30-89 Days Past Due	23,643	47,161
Nonaccrual	23,276	25,519
Loans and leases, net of unearned discount	7,754,693	7,075,323
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,429,573	4,007,349
30-89 Days Past Due	30,521	55,498
Nonaccrual	31,090	39,404
Loans and leases, net of unearned discount	4,491,184	4,102,251
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,428,524	1,346,868
30-89 Days Past Due	15,157	17,561
Accruing Loans Past Due 90 Days or More	3,055	4,581
Nonaccrual	42,257	38,231
Loans and leases, net of unearned discount	$ 1,488,993	$ 1,407,241