Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 86,596,936	$ 87,968,321
30-89 Days Past Due	892,705	1,025,245
Accruing Loans Past Due 90 Days or More	280,019	300,659
Purchased Impaired	552,935	578,032
Nonaccrual	926,675	920,015
Loans and leases, net of unearned discount	89,313,002	90,853,416
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	63,732	61,144
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,986,926	22,287,857
30-89 Days Past Due	38,046	53,503
Accruing Loans Past Due 90 Days or More	6,695	6,195
Purchased Impaired	1,825	641
Nonaccrual	261,497	261,434
Loans and leases, net of unearned discount	22,295,376	22,610,047
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	387	417
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,088,525	25,076,684
30-89 Days Past Due	185,331	183,531
Accruing Loans Past Due 90 Days or More	17,322	7,054
Purchased Impaired	26,391	31,404
Nonaccrual	183,113	176,201
Loans and leases, net of unearned discount	25,514,300	25,487,744
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	13,618	12,870
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,714,177	1,884,989
30-89 Days Past Due	15,185	4,667
Accruing Loans Past Due 90 Days or More		5
Purchased Impaired	12,798	14,006
Nonaccrual	13,573	16,707
Loans and leases, net of unearned discount	1,757,705	1,922,326
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	1,972	1,952
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,747,834	5,985,118
30-89 Days Past Due	23,973	77,701
Accruing Loans Past Due 90 Days or More		922
Purchased Impaired	13,879	14,274
Nonaccrual	13,963	18,111
Loans and leases, net of unearned discount	5,799,649	6,096,324
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
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	17,004,912	17,631,377
30-89 Days Past Due	431,427	485,468
Accruing Loans Past Due 90 Days or More	251,308	281,298
Purchased Impaired	362,283	378,549
Nonaccrual	237,685	229,242
Loans and leases, net of unearned discount	18,298,731	19,017,471
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	11,116	11,537
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,086,264	3,239,344
30-89 Days Past Due	91,177	88,366
Purchased Impaired	135,759	139,158
Nonaccrual	112,560	106,573
Loans and leases, net of unearned discount	3,425,760	3,573,441
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,398,590	5,502,091
30-89 Days Past Due	32,939	44,565
Nonaccrual	79,962	81,815
Loans and leases, net of unearned discount	5,523,729	5,641,149
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	12,238	12,678
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,049,712	2,869,232
30-89 Days Past Due	48,751	56,158
Nonaccrual	16,109	18,674
Loans and leases, net of unearned discount	3,114,572	2,944,065
Automobile [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More		1
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,519,996	3,491,629
30-89 Days Past Due	25,876	31,286
Accruing Loans Past Due 90 Days or More	4,694	5,185
Nonaccrual	8,213	11,258
Loans and leases, net of unearned discount	3,583,180	3,560,849
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 24,401	$ 21,491