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, 2014		Dec. 31, 2013
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,000,222
Expires After One Year	137,499
Total Amount Outstanding	1,137,721	[1]	975,968	[1]
Maximum Amount of Future Payments	1,137,721
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	936,790
Expires After One Year	129,337
Total Amount Outstanding	1,066,127
Maximum Amount of Future Payments	1,066,127
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	57,058
Expires After One Year	8,162
Total Amount Outstanding	65,220
Maximum Amount of Future Payments	65,220
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	6,374
Expires After One Year	0
Total Amount Outstanding	6,374
Maximum Amount of Future Payments	$ 6,374

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