Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 84,952,569	$ 84,400,551
30-89 Days past due	929,395	1,135,296
Accruing loans past due 90 days or more	336,170	317,441
Purchased impaired	715,874	768,329
Nonaccrual	876,691	799,409
Loans and leases, net of unearned discount	87,872,466	87,489,499
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	20,911,645	20,122,648
30-89 Days past due	30,495	52,868
Accruing loans past due 90 days or more	2,358	2,310
Purchased impaired	1,765	1,902
Nonaccrual	279,790	241,917
Loans and leases, net of unearned discount	21,226,577	20,422,338
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	23,740,729	23,645,354
30-89 Days past due	149,108	172,439
Accruing loans past due 90 days or more	41,776	12,963
Purchased impaired	39,840	46,790
Nonaccrual	171,256	179,606
Loans and leases, net of unearned discount	24,149,527	24,065,942
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,747,261	1,507,856
30-89 Days past due	15,304	7,969
Accruing loans past due 90 days or more	195	5,760
Purchased impaired	23,516	28,734
Nonaccrual	32,458	28,429
Loans and leases, net of unearned discount	1,822,227	1,585,673
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,663,835	3,428,939
30-89 Days past due	28,336	65,932
Accruing loans past due 90 days or more	9,068	7,936
Purchased impaired	19,239	24,525
Nonaccrual	20,781	16,363
Loans and leases, net of unearned discount	3,741,539	3,545,696
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	19,747,097	20,507,551
30-89 Days past due	500,241	560,312
Accruing loans past due 90 days or more	278,640	284,451
Purchased impaired	463,871	488,599
Nonaccrual	186,452	153,281
Loans and leases, net of unearned discount	21,192,091	22,010,273
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,757,924	3,885,073
30-89 Days past due	107,679	137,289
Accruing loans past due 90 days or more	275
Purchased impaired	165,404	175,518
Nonaccrual	76,265	61,950
Loans and leases, net of unearned discount	4,107,547	4,259,830
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,720,342	5,805,222
30-89 Days past due	40,054	45,604
Purchased impaired	2,239	2,261
Nonaccrual	78,722	84,467
Loans and leases, net of unearned discount	5,857,255	5,952,776
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,580,241	2,446,473
30-89 Days past due	33,439	56,181
Nonaccrual	14,817	16,597
Loans and leases, net of unearned discount	2,628,499	2,519,257
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,083,495	3,051,435
30-89 Days past due	24,739	36,702
Accruing loans past due 90 days or more	3,858	4,021
Nonaccrual	16,150	16,799
Loans and leases, net of unearned discount	3,147,204	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	61,767	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	524	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	6,818	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	3,493	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	15,790	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	15,898	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	2	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	$ 18,962	$ 18,757