Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,236,039
Expires After One Year	80,419
Total Amount Outstanding	1,316,458	$ 1,254,338
Maximum Amount of Future Payments	1,316,458
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,176,681
Expires After One Year	68,629
Total Amount Outstanding	1,245,310
Maximum Amount of Future Payments	1,245,310
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	47,756
Expires After One Year	11,790
Total Amount Outstanding	59,546
Maximum Amount of Future Payments	59,546
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	11,602
Expires After One Year	0
Total Amount Outstanding	11,602
Maximum Amount of Future Payments	$ 11,602