Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 818,563
Expires After One Year	62,560
Total Amount Outstanding	881,123	[1]	842,091	[1]
Maximum Amount of Future Payments	881,123
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	760,135
Expires After One Year	52,889
Total Amount Outstanding	813,024
Maximum Amount of Future Payments	813,024
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	52,594
Expires After One Year	9,671
Total Amount Outstanding	62,265
Maximum Amount of Future Payments	62,265
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	5,834
Expires After One Year	0
Total Amount Outstanding	5,834
Maximum Amount of Future Payments	$ 5,834

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