Allowance for credit losses - Summary of Loan Grades (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 66,570,957	$ 60,096,005
Commercial, Financial, Leasing, etc [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,776,953	15,734,436
Commercial, Financial, Leasing, etc [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,889,753	14,869,636
Commercial, Financial, Leasing, etc [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	735,292	701,202
Commercial, Financial, Leasing, etc [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	151,908	163,598
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,273,173	20,259,448
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,275,182	19,089,252
Commercial [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	804,132	999,085
Commercial [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	193,859	171,111
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,189,526	1,508,333
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	922,141	1,085,970
Residential Builder and Developer [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	85,520	140,787
Residential Builder and Developer [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	181,865	281,576
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,531,091	2,643,333
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,307,436	2,254,609
Other Commercial Construction [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	186,843	282,399
Other Commercial Construction [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 36,812	$ 106,325