Loans and leases and the allowance for credit losses - Summary of Loan Grades (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
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] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	15,823,813	14,869,636
Commercial, financial, leasing, etc [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	758,956	701,202
Commercial, financial, leasing, etc [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	121,806	163,598
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,460,221	20,259,448
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,373,273	19,089,252
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	914,702	999,085
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	172,246	171,111
Residential builder and developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,306,352	1,508,333
Residential builder and developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	976,233	1,085,970
Residential builder and developer [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	104,590	140,787
Residential builder and developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	225,529	281,576
Other commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,203,843	2,643,333
Other commercial construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,966,097	2,254,609
Other commercial construction [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	211,037	282,399
Other commercial construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 26,709	$ 106,325