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
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 925,860	$ 908,290
Provision for credit losses	38,000	49,000
Net charge-offs
Charge-offs	(48,948)	(60,276)
Recoveries	12,205	11,992
Net charge-offs	(36,743)	(48,284)
Ending balance	927,117	909,006
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	246,759	234,022
Provision for credit losses	17,880	10,121
Net charge-offs
Charge-offs	(9,544)	(8,037)
Recoveries	2,756	3,167
Net charge-offs	(6,788)	(4,870)
Ending balance	257,851	239,273
Real Estate Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	337,101	367,637
Provision for credit losses	(312)	(2,260)
Net charge-offs
Charge-offs	(9,588)	(10,540)
Recoveries	815	1,717
Net charge-offs	(8,773)	(8,823)
Ending balance	328,016	356,554
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	88,807	91,915
Provision for credit losses	5,036	16,230
Net charge-offs
Charge-offs	(8,171)	(12,718)
Recoveries	4,450	1,874
Net charge-offs	(3,721)	(10,844)
Ending balance	90,122	97,301
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	179,418	143,121
Provision for credit losses	14,836	23,538
Net charge-offs
Charge-offs	(21,645)	(28,981)
Recoveries	4,184	5,234
Net charge-offs	(17,461)	(23,747)
Ending balance	176,793	142,912
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	73,775	71,595
Provision for credit losses	560	1,371
Net charge-offs
Ending balance	$ 74,335	$ 72,966