Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 86,867,022	$ 84,400,551
30-89 days past due	942,653	1,135,296
Accruing loans past due 90 days or more	317,282	317,441
Purchased impaired	616,991	768,329
Nonaccrual	837,362	799,409
Loans and leases, net of unearned discount	89,646,492	87,489,499
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	65,182	68,473
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,601,646	20,122,648
30-89 days past due	70,597	52,868
Accruing loans past due 90 days or more	10,831	2,310
Purchased impaired	795	1,902
Nonaccrual	231,401	241,917
Loans and leases, net of unearned discount	21,917,163	20,422,338
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	1,893	693
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,283,146	23,111,673
30-89 days past due	116,651	172,439
Accruing loans past due 90 days or more	15,926	12,963
Purchased impaired	32,775	46,790
Nonaccrual	157,527	179,606
Loans and leases, net of unearned discount	24,619,317	23,532,261
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	13,292	8,790
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,814,299	1,507,856
30-89 days past due	16,993	7,969
Accruing loans past due 90 days or more	4,476	5,760
Purchased impaired	18,096	28,734
Nonaccrual	20,118	28,429
Loans and leases, net of unearned discount	1,877,244	1,585,673
Residential Builder and Developer [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	3,262	6,925
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,525,684	3,962,620
30-89 days past due	20,238	65,932
Accruing loans past due 90 days or more		7,936
Purchased impaired	15,412	24,525
Nonaccrual	20,669	16,363
Loans and leases, net of unearned discount	5,582,201	4,079,377
Other Commercial Construction [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	198	2,001
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	18,438,396	20,507,551
30-89 days past due	494,767	560,312
Accruing loans past due 90 days or more	281,023	284,451
Purchased impaired	401,551	488,599
Nonaccrual	213,896	153,281
Loans and leases, net of unearned discount	19,842,143	22,010,273
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	12,510	16,079
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,400,578	3,885,073
30-89 days past due	105,621	137,289
Purchased impaired	146,722	175,518
Nonaccrual	89,356	61,950
Loans and leases, net of unearned discount	3,742,277	4,259,830
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,586,704	5,805,222
30-89 days past due	40,406	45,604
Purchased impaired	1,640	2,261
Nonaccrual	79,623	84,467
Loans and leases, net of unearned discount	5,721,387	5,952,776
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	13,014	15,222
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,805,779	2,446,473
30-89 days past due	46,347	56,181
Nonaccrual	14,453	16,597
Loans and leases, net of unearned discount	2,866,583	2,519,257
Automobile [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	4	6
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,410,790	3,051,435
30-89 days past due	31,033	36,702
Accruing loans past due 90 days or more	5,026	4,021
Nonaccrual	10,319	16,799
Loans and leases, net of unearned discount	3,478,177	3,127,714
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	$ 21,009	$ 18,757