Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 86,916,076	$ 86,140,950
30-89 Days Past Due	1,146,477	866,337
Accruing Loans Past Due 90 Days or More	461,162	222,527
Purchased Impaired	253,496	303,305
Nonaccrual	1,005,249	893,608
Loans and leases, net of unearned discount	89,823,193	88,466,477
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	40,733	39,750
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	22,689,923	22,701,020
30-89 Days Past Due	125,742	39,798
Accruing Loans Past Due 90 Days or More	2,898	2,567
Nonaccrual	382,809	234,423
Loans and leases, net of unearned discount	23,201,372	22,977,976
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		168
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,613,988	25,250,983
30-89 Days Past Due	186,157	134,474
Accruing Loans Past Due 90 Days or More	8,387	11,457
Purchased Impaired	14,406	9,769
Nonaccrual	184,632	203,672
Loans and leases, net of unearned discount	26,007,585	25,610,365
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	15	10
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,546,570	1,665,178
30-89 Days Past Due	6,300	20,333
Purchased Impaired	639
Nonaccrual	4,975	4,798
Loans and leases, net of unearned discount	1,558,484	1,690,309
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,229,925	6,982,077
30-89 Days Past Due	112,651	43,615
Accruing Loans Past Due 90 Days or More	4,291	14,344
Purchased Impaired	854	641
Nonaccrual	31,441	22,205
Loans and leases, net of unearned discount	7,379,162	7,062,882
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	12,975,992	13,591,790
30-89 Days Past Due	495,831	404,808
Accruing Loans Past Due 90 Days or More	439,649	189,682
Purchased Impaired	162,475	203,044
Nonaccrual	223,566	233,352
Loans and leases, net of unearned discount	14,302,759	14,629,326
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	5,246	6,650
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,968,580	2,278,040
30-89 Days Past Due	72,815	72,544
Purchased Impaired	75,122	89,851
Nonaccrual	81,679	84,685
Loans and leases, net of unearned discount	2,198,196	2,525,120
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,486,664	4,758,513
30-89 Days Past Due	29,826	25,416
Nonaccrual	59,915	71,292
Loans and leases, net of unearned discount	4,579,792	4,860,254
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	3,387	5,033
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,262,857	4,085,781
30-89 Days Past Due	27,880	29,947
Nonaccrual	11,852	11,199
Loans and leases, net of unearned discount	5,302,589	4,127,162
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		235
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,767,965	3,555,757
30-89 Days Past Due	74,504	79,804
Nonaccrual	21,039	23,359
Loans and leases, net of unearned discount	3,863,508	3,658,920
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,373,612	1,271,811
30-89 Days Past Due	14,771	15,598
Accruing Loans Past Due 90 Days or More	5,937	4,477
Nonaccrual	3,341	4,623
Loans and leases, net of unearned discount	1,429,746	1,324,163
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 32,085	$ 27,654