Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 792,402
Expires After One Year	63,096
Total Amount Outstanding	855,498	[1]	842,091	[1]
Maximum Amount of Future Payments	855,498
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	737,914
Expires After One Year	50,881
Total Amount Outstanding	788,795
Maximum Amount of Future Payments	788,795
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	48,218
Expires After One Year	12,215
Total Amount Outstanding	60,433
Maximum Amount of Future Payments	60,433
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	6,270
Expires After One Year	0
Total Amount Outstanding	6,270
Maximum Amount of Future Payments	$ 6,270

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