Loans and leases and the allowance for credit losses - Changes in Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 917,028	$ 907,589	$ 908,290	$ 902,941
Provision for credit losses	46,000	58,000	155,000	196,000
Charge-offs	(50,096)	(66,496)	(174,534)	(221,240)
Recoveries	8,291	9,432	32,467	30,824
Net charge-offs	(41,805)	(57,064)	(142,067)	(190,416)
Ending balance	921,223	908,525	921,223	908,525
Commercial, financial, leasing, etc [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	244,728	209,879	234,022	212,579
Provision for credit losses	439	23,145	29,663	44,957
Charge-offs	(8,874)	(12,073)	(32,989)	(41,023)
Recoveries	1,174	2,613	6,771	7,051
Net charge-offs	(7,700)	(9,460)	(26,218)	(33,972)
Ending balance	237,467	223,564	237,467	223,564
Real Estate Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	341,521	401,111	367,637	400,562
Provision for credit losses	9,891	(545)	4,322	36,965
Charge-offs	(7,982)	(13,712)	(31,578)	(54,206)
Recoveries	1,421	839	4,470	4,372
Net charge-offs	(6,561)	(12,873)	(27,108)	(49,834)
Ending balance	344,851	387,693	344,851	387,693
Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	93,269	87,341	91,915	86,351
Provision for credit losses	8,247	8,264	30,064	37,759
Charge-offs	(8,687)	(12,135)	(32,812)	(44,174)
Recoveries	1,139	1,750	4,801	5,284
Net charge-offs	(7,548)	(10,385)	(28,011)	(38,890)
Ending balance	93,968	85,220	93,968	85,220
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	164,352	137,309	143,121	133,067
Provision for credit losses	26,962	27,231	88,927	74,847
Charge-offs	(24,553)	(28,576)	(77,155)	(81,837)
Recoveries	4,557	4,230	16,425	14,117
Net charge-offs	(19,996)	(24,346)	(60,730)	(67,720)
Ending balance	171,318	140,194	171,318	140,194
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	73,158	71,949	71,595	70,382
Provision for credit losses	461	(95)	2,024	1,472
Charge-offs
Recoveries
Net charge-offs
Ending balance	$ 73,619	$ 71,854	$ 73,619	$ 71,854