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	Mar. 31, 2015		Dec. 31, 2014
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,611,025	[1]	$ 1,591,408	[1]
Variable interest rate commitments	12,618,196	[1]	11,860,039	[1]
Total loan commitments available for funding	14,229,221	[1]	13,451,447	[1]
Commercial and standby letters of credit	1,256,293	[2]	1,254,338	[2]
Total unfunded credit commitments	15,485,514		14,705,785
Commitments unavailable for funding	1,920,937	[3]	1,868,489	[3]
Maximum lending limits for accounts receivable factoring arrangements	1,120,763	[4]	1,044,548	[4]
Reserve for unfunded credit commitments	$ 38,628	[5]	$ 36,419	[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.