Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Supply Commitment [Line Items]
Fixed interest rate commitments	$ 733,795	[1]	$ 658,377	[1]
Variable interest rate commitments	6,328,420	[1]	6,548,002	[1]
Total loan commitments available for funding	7,062,215	[1]	7,206,379	[1]
Commercial and standby letters of credit	803,922	[2]	861,191	[2]
Total unfunded credit commitments	7,866,137		8,067,570
Commitments unavailable for funding	900,248	[3]	841,439	[3]
Maximum lending limits for accounts receivable factoring arrangements	812,004	[4]	747,392	[4]
Reserve for unfunded credit commitments	$ 21,553	[5]	$ 21,811	[5]

[1] Represents commitments which are available for funding, due to clients meeting all collateral, compliance and financial covenants required under loan commitment agreements.

[2] See below for additional information on our commercial and standby letters of credit.

[3] Represents commitments which are currently unavailable for funding, due to clients failing to meet all collateral, compliance and financial covenants under loan commitment agreements.

[4] We extend credit under accounts receivable factoring arrangements when our clients' sales invoices are deemed creditworthy under existing underwriting practices.

[5] Our reserve for unfunded credit commitments includes an allowance for both our unfunded loan commitments and our letters of credit.