Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,222,651	[1]	$ 862,120	[1]
Variable interest rate commitments	8,571,795	[1]	6,906,580	[1]
Total loan commitments available for funding	9,794,446	[1]	7,768,700	[1]
Commercial and standby letters of credit	881,123	[2]	842,091	[2]
Total unfunded credit commitments	10,675,569		8,610,791
Commitments unavailable for funding	1,340,102	[3]	1,315,072	[3]
Maximum lending limits for accounts receivable factoring arrangements	873,502	[4]	880,057	[4]
Reserve for unfunded credit commitments	$ 28,456	[5]	$ 22,299	[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.