Loans and leases and the allowance for credit losses - Loans and leases receivable net of deferred income by impairment methodology (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 64,111,955	$ 60,096,005
Individually evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	985,108	1,110,873
Collectively evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	62,598,846	58,331,770
Purchased impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	528,001	653,362
Commercial, financial, leasing, etc [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,704,575	15,734,436
Commercial, financial, leasing, etc [Member] | Individually evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	129,916	171,442
Commercial, financial, leasing, etc [Member] | Collectively evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,557,225	15,539,232
Commercial, financial, leasing, etc [Member] | Purchased impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,434	23,762
Commercial real estate loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	24,970,416	24,411,114
Commercial real estate loans [Member] | Individually evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	488,493	561,615
Commercial real estate loans [Member] | Collectively evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	24,016,884	23,281,585
Commercial real estate loans [Member] | Purchased impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	465,039	567,914
Residential real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,808,220	7,923,165
Residential real estate [Member] | Individually evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	290,023	306,320
Residential real estate [Member] | Collectively evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,476,900	7,560,104
Residential real estate [Member] | Purchased impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	41,297	56,741
Consumer loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,628,744	12,027,290
Consumer loans [Member] | Individually evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	76,676	71,496
Consumer loans [Member] | Collectively evaluated for impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,547,837	11,950,849
Consumer loans [Member] | Purchased impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 4,231	$ 4,945