Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 86,347,768	$ 87,968,321
30-89 Days Past Due	1,025,061	1,025,245
Accruing Loans Past Due 90 Days or More	265,461	300,659
Purchased Impaired	512,393	578,032
Nonaccrual	872,374	920,015
Loans and leases, net of unearned discount	89,080,555	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	57,498	61,144
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,936,863	22,287,857
30-89 Days Past Due	49,066	53,503
Accruing Loans Past Due 90 Days or More	1,126	6,195
Purchased Impaired	2,307	641
Nonaccrual	201,295	261,434
Loans and leases, net of unearned discount	22,191,051	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	394	417
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	25,237,177	25,076,684
30-89 Days Past Due	256,218	183,531
Accruing Loans Past Due 90 Days or More	19,187	7,054
Purchased Impaired	24,518	31,404
Nonaccrual	201,518	176,201
Loans and leases, net of unearned discount	25,750,262	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	11,644	12,870
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,639,210	1,884,989
30-89 Days Past Due	11,172	4,667
Accruing Loans Past Due 90 Days or More		5
Purchased Impaired	10,960	14,006
Nonaccrual	7,389	16,707
Loans and leases, net of unearned discount	1,670,536	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	1,805	1,952
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,808,838	5,985,118
30-89 Days Past Due	83,700	77,701
Accruing Loans Past Due 90 Days or More	7,481	922
Purchased Impaired	12,209	14,274
Nonaccrual	15,965	18,111
Loans and leases, net of unearned discount	5,928,193	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	16,438,548	17,631,377
30-89 Days Past Due	424,098	485,468
Accruing Loans Past Due 90 Days or More	233,081	281,298
Purchased Impaired	336,177	378,549
Nonaccrual	236,813	229,242
Loans and leases, net of unearned discount	17,676,687	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	7,970	11,537
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,968,241	3,239,344
30-89 Days Past Due	82,569	88,366
Accruing Loans Past Due 90 Days or More	300
Purchased Impaired	126,222	139,158
Nonaccrual	106,152	106,573
Loans and leases, net of unearned discount	3,283,484	3,573,441
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,337,934	5,502,091
30-89 Days Past Due	32,378	44,565
Accruing Loans Past Due 90 Days or More	773
Nonaccrual	77,471	81,815
Loans and leases, net of unearned discount	5,460,188	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	11,632	12,678
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,166,912	2,869,232
30-89 Days Past Due	59,243	56,158
Nonaccrual	17,154	18,674
Loans and leases, net of unearned discount	3,243,310	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	1
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,814,045	3,491,629
30-89 Days Past Due	26,617	31,286
Accruing Loans Past Due 90 Days or More	3,513	5,185
Nonaccrual	8,617	11,258
Loans and leases, net of unearned discount	3,876,844	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	$ 24,052	$ 21,491