Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,313,260
Expires After One Year	78,552
Total Amount Outstanding	1,391,812	$ 1,254,338
Maximum Amount of Future Payments	1,391,812
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,251,147
Expires After One Year	68,343
Total Amount Outstanding	1,319,490
Maximum Amount of Future Payments	1,319,490
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	50,220
Expires After One Year	10,209
Total Amount Outstanding	60,429
Maximum Amount of Future Payments	60,429
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	11,893
Expires After One Year	0
Total Amount Outstanding	11,893
Maximum Amount of Future Payments	$ 11,893