Loans and leases and the allowance for credit losses - Impaired Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 992,531	$ 1,123,315
Unpaid Principal Balance	1,292,410	1,440,333
Related Allowance	137,102	168,001
Commercial, financial, leasing, etc [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	130,089	171,642
Unpaid Principal Balance	158,367	206,288
Related Allowance	29,911	48,674
Commercial real estate loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	178,336	174,522
Unpaid Principal Balance	228,116	219,574
Related Allowance	18,734	17,651
Residential builder and developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	229,500	292,449
Unpaid Principal Balance	377,488	458,146
Related Allowance	34,228	52,562
Other commercial construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	86,459	106,886
Unpaid Principal Balance	90,665	114,501
Related Allowance	7,749	3,836
Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	125,936	121,568
Unpaid Principal Balance	152,493	145,123
Related Allowance	5,027	4,420
Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	165,576	184,752
Unpaid Principal Balance	207,373	223,920
Related Allowance	19,000	25,000
Home equity lines and loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	12,362	9,385
Unpaid Principal Balance	13,635	10,670
Related Allowance	2,187	2,306
Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	50,886	53,710
Unpaid Principal Balance	50,886	53,710
Related Allowance	15,012	11,468
Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	13,387	8,401
Unpaid Principal Balance	13,387	8,401
Related Allowance	5,254	2,084
Impaired financing receivable with recorded allowance [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	733,583	724,725
Unpaid Principal Balance	942,486	934,731
Related Allowance	137,102	168,001
Impaired financing receivable with recorded allowance [Member] | Commercial, financial, leasing, etc [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	106,448	118,538
Unpaid Principal Balance	126,156	145,510
Related Allowance	29,911	48,674
Impaired financing receivable with recorded allowance [Member] | Commercial real estate loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	107,669	102,886
Unpaid Principal Balance	135,663	128,456
Related Allowance	18,734	17,651
Impaired financing receivable with recorded allowance [Member] | Residential builder and developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	134,298	159,293
Unpaid Principal Balance	260,010	280,869
Related Allowance	34,228	52,562
Impaired financing receivable with recorded allowance [Member] | Other commercial construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	74,306	20,234
Unpaid Principal Balance	77,938	24,639
Related Allowance	7,749	3,836
Impaired financing receivable with recorded allowance [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	103,184	101,882
Unpaid Principal Balance	121,141	119,498
Related Allowance	5,027	4,420
Impaired financing receivable with recorded allowance [Member] | Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	131,043	150,396
Unpaid Principal Balance	143,670	162,978
Related Allowance	19,000	25,000
Impaired financing receivable with recorded allowance [Member] | Home equity lines and loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	12,362	9,385
Unpaid Principal Balance	13,635	10,670
Related Allowance	2,187	2,306
Impaired financing receivable with recorded allowance [Member] | Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	50,886	53,710
Unpaid Principal Balance	50,886	53,710
Related Allowance	15,012	11,468
Impaired financing receivable with recorded allowance [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	13,387	8,401
Unpaid Principal Balance	13,387	8,401
Related Allowance	5,254	2,084
Impaired financing receivable with no related allowance [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	258,948	398,590
Unpaid Principal Balance	349,924	505,602
Impaired financing receivable with no related allowance [Member] | Commercial, financial, leasing, etc [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	23,641	53,104
Unpaid Principal Balance	32,211	60,778
Impaired financing receivable with no related allowance [Member] | Commercial real estate loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	70,667	71,636
Unpaid Principal Balance	92,453	91,118
Impaired financing receivable with no related allowance [Member] | Residential builder and developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	95,202	133,156
Unpaid Principal Balance	117,478	177,277
Impaired financing receivable with no related allowance [Member] | Other commercial construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	12,153	86,652
Unpaid Principal Balance	12,727	89,862
Impaired financing receivable with no related allowance [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	22,752	19,686
Unpaid Principal Balance	31,352	25,625
Impaired financing receivable with no related allowance [Member] | Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	34,533	34,356
Unpaid Principal Balance	$ 63,703	$ 60,942