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, 2015		Dec. 31, 2014
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,191,746
Expires After One Year	64,547
Total Amount Outstanding	1,256,293	[1]	1,254,338	[1]
Maximum Amount of Future Payments	1,256,293
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,137,234
Expires After One Year	57,997
Total Amount Outstanding	1,195,231
Maximum Amount of Future Payments	1,195,231
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	45,105
Expires After One Year	6,550
Total Amount Outstanding	51,655
Maximum Amount of Future Payments	51,655
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	9,407
Expires After One Year	0
Total Amount Outstanding	9,407
Maximum Amount of Future Payments	$ 9,407

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