Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Disclosure Summary Information Related To Commitments To Extend Credit [Abstract]
Fixed interest rate commitments	$ 855,885	[1]	$ 658,377	[1]
Variable interest rate commitments	6,965,078	[1]	6,548,002	[1]
Total loan commitments available for funding	7,820,963	[1]	7,206,379	[1]
Commercial and standby letters of credit	889,265	[2]	861,191	[2]
Total unfunded credit commitments	8,710,228		8,067,570
Commitments unavailable for funding	994,888		841,439
Maximum lending limits for accounts receivable factoring arrangements	888,463	[3]	747,392	[3]
Reserve for unfunded credit commitments	$ 23,075	[4]	$ 21,811	[4]

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

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