Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 770,401
Expires After One Year	65,550
Total Amount Outstanding	835,951	[1]	842,091	[1]
Maximum Amount of Future Payments	835,951
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	713,950
Expires After One Year	55,950
Total Amount Outstanding	769,900
Maximum Amount of Future Payments	769,900
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	48,651
Expires After One Year	9,600
Total Amount Outstanding	58,251
Maximum Amount of Future Payments	58,251
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	7,800
Expires After One Year	0
Total Amount Outstanding	7,800
Maximum Amount of Future Payments	$ 7,800

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