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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 927,117	$ 909,006	$ 925,860	$ 908,290
Provision for credit losses	57,000	60,000	95,000	109,000
Net charge-offs
Charge-offs	(76,626)	(64,162)	(125,574)	(124,438)
Recoveries	19,574	12,184	31,779	24,176
Net charge-offs	(57,052)	(51,978)	(93,795)	(100,262)
Ending balance	927,065	917,028	927,065	917,028
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	257,851	239,273	246,759	234,022
Provision for credit losses	55,647	19,103	73,527	29,224
Net charge-offs
Charge-offs	(46,312)	(16,078)	(55,856)	(24,115)
Recoveries	1,681	2,430	4,437	5,597
Net charge-offs	(44,631)	(13,648)	(51,419)	(18,518)
Ending balance	268,867	244,728	268,867	244,728
Real Estate Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,016	356,554	337,101	367,637
Provision for credit losses	(10,913)	(3,309)	(11,225)	(5,569)
Net charge-offs
Charge-offs	(4,204)	(13,056)	(13,792)	(23,596)
Recoveries	11,365	1,332	12,180	3,049
Net charge-offs	7,161	(11,724)	(1,612)	(20,547)
Ending balance	324,264	341,521	324,264	341,521
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	90,122	97,301	88,807	91,915
Provision for credit losses	(1,438)	5,587	3,598	21,817
Net charge-offs
Charge-offs	(5,092)	(11,407)	(13,263)	(24,125)
Recoveries	1,719	1,788	6,169	3,662
Net charge-offs	(3,373)	(9,619)	(7,094)	(20,463)
Ending balance	85,311	93,269	85,311	93,269
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	176,793	142,912	179,418	143,121
Provision for credit losses	13,707	38,427	28,543	61,965
Net charge-offs
Charge-offs	(21,018)	(23,621)	(42,663)	(52,602)
Recoveries	4,809	6,634	8,993	11,868
Net charge-offs	(16,209)	(16,987)	(33,670)	(40,734)
Ending balance	174,291	164,352	174,291	164,352
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	74,335	72,966	73,775	71,595
Provision for credit losses	(3)	192	557	1,563
Net charge-offs
Charge-offs
Recoveries
Net charge-offs
Ending balance	$ 74,332	$ 73,158	$ 74,332	$ 73,158