Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 85,715,365	$ 84,400,551
30-89 Days past due	928,679	1,135,296
Accruing loans past due 90 days or more	298,449	317,441
Purchased impaired	662,059	768,329
Nonaccrual	848,855	799,409
Loans and leases, net of unearned discount	88,521,998	87,489,499
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,157,606	20,122,648
30-89 Days past due	63,069	52,868
Accruing loans past due 90 days or more	6,665	2,310
Purchased impaired	766	1,902
Nonaccrual	240,684	241,917
Loans and leases, net of unearned discount	21,469,242	20,422,338
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	23,390,039	23,111,673
30-89 Days past due	125,657	172,439
Accruing loans past due 90 days or more	16,487	12,963
Purchased impaired	36,111	46,790
Nonaccrual	172,670	179,606
Loans and leases, net of unearned discount	23,754,899	23,532,261
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,819,984	1,507,856
30-89 Days past due	14,892	7,969
Accruing loans past due 90 days or more		5,760
Purchased impaired	19,972	28,734
Nonaccrual	24,263	28,429
Loans and leases, net of unearned discount	1,883,958	1,585,673
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,993,493	3,962,620
30-89 Days past due	41,297	65,932
Accruing loans past due 90 days or more		7,936
Purchased impaired	16,009	24,525
Nonaccrual	21,294	16,363
Loans and leases, net of unearned discount	5,072,373	4,079,377
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	19,208,724	20,507,551
30-89 Days past due	470,646	560,312
Accruing loans past due 90 days or more	270,845	284,451
Purchased impaired	433,192	488,599
Nonaccrual	202,949	153,281
Loans and leases, net of unearned discount	20,599,443	22,010,273
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,584,715	3,885,073
30-89 Days past due	112,743	137,289
Purchased impaired	154,320	175,518
Nonaccrual	79,028	61,950
Loans and leases, net of unearned discount	3,930,806	4,259,830
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,658,417	5,805,222
30-89 Days past due	34,735	45,604
Purchased impaired	1,689	2,261
Nonaccrual	86,870	84,467
Loans and leases, net of unearned discount	5,796,319	5,952,776
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,669,708	2,446,473
30-89 Days past due	39,139	56,181
Nonaccrual	12,390	16,597
Loans and leases, net of unearned discount	2,721,238	2,519,257
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,232,679	3,051,435
30-89 Days past due	26,501	36,702
Accruing loans past due 90 days or more	4,452	4,021
Nonaccrual	8,707	16,799
Loans and leases, net of unearned discount	3,293,720	3,127,714
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	68,591	68,473
Accruing Loans Acquired at Discount [Member] | Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	452	693
Accruing Loans Acquired at Discount [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	13,935	8,790
Accruing Loans Acquired at Discount [Member] | Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	4,847	6,925
Accruing Loans Acquired at Discount [Member] | Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	280	2,001
Accruing Loans Acquired at Discount [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	13,087	16,079
Accruing Loans Acquired at Discount [Member] | Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	14,608	15,222
Accruing Loans Acquired at Discount [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	1	6
Accruing Loans Acquired at Discount [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing loans past due 90 days or more	$ 21,381	$ 18,757