Loans and leases and the allowance for credit losses - Summary of Loan Grades (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 65,924,267	$ 66,570,957
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,469,138	17,776,953
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,590,137	16,889,753
Commercial, Financial, Leasing, etc. [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	674,802	735,292
Commercial, Financial, Leasing, etc. [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	204,199	151,908
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,058,740	22,273,173
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,086,718	21,275,182
Commercial [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	785,783	804,132
Commercial [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	186,239	193,859
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,166,648	1,189,526
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	929,857	922,141
Residential Builder and Developer [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	69,995	85,520
Residential Builder and Developer [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	166,796	181,865
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,719,431	2,531,091
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,533,617	2,307,436
Other Commercial Construction [Member] | Criticized accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	145,644	186,843
Other Commercial Construction [Member] | Criticized nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 40,170	$ 36,812