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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 927,065	$ 917,028	$ 925,860	$ 908,290
Provision for credit losses	48,000	46,000	143,000	155,000
Allowance related to loans securitized and sold	(11,000)		(11,000)
Net charge-offs
Charge-offs	(64,194)	(50,096)	(189,768)	(174,534)
Recoveries	16,499	8,291	48,278	32,467
Net charge-offs	(47,695)	(41,805)	(141,490)	(142,067)
Ending balance	916,370	921,223	916,370	921,223
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	268,867	244,728	246,759	234,022
Provision for credit losses	20,209	439	93,736	29,663
Allowance related to loans securitized and sold
Net charge-offs
Charge-offs	(30,931)	(8,874)	(86,787)	(32,989)
Recoveries	5,150	1,174	9,587	6,771
Net charge-offs	(25,781)	(7,700)	(77,200)	(26,218)
Ending balance	263,295	237,467	263,295	237,467
Real Estate Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	324,264	341,521	337,101	367,637
Provision for credit losses	12,139	9,891	914	4,322
Allowance related to loans securitized and sold
Net charge-offs
Charge-offs	(7,701)	(7,982)	(21,493)	(31,578)
Recoveries	4,751	1,421	16,931	4,470
Net charge-offs	(2,950)	(6,561)	(4,562)	(27,108)
Ending balance	333,453	344,851	333,453	344,851
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	85,311	93,269	88,807	91,915
Provision for credit losses	315	8,247	3,913	30,064
Allowance related to loans securitized and sold
Net charge-offs
Charge-offs	(5,320)	(8,687)	(18,583)	(32,812)
Recoveries	2,399	1,139	8,568	4,801
Net charge-offs	(2,921)	(7,548)	(10,015)	(28,011)
Ending balance	82,705	93,968	82,705	93,968
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	174,291	164,352	179,418	143,121
Provision for credit losses	14,935	26,962	43,478	88,927
Allowance related to loans securitized and sold	(11,000)		(11,000)
Net charge-offs
Charge-offs	(20,242)	(24,553)	(62,905)	(77,155)
Recoveries	4,199	4,557	13,192	16,425
Net charge-offs	(16,043)	(19,996)	(49,713)	(60,730)
Ending balance	162,183	171,318	162,183	171,318
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	74,332	73,158	73,775	71,595
Provision for credit losses	402	461	959	2,024
Allowance related to loans securitized and sold
Net charge-offs
Charge-offs
Recoveries
Net charge-offs
Ending balance	$ 74,734	$ 73,619	$ 74,734	$ 73,619