Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,707,434
Expires After One Year	69,803
Total Amount Outstanding	1,777,237	$ 1,695,856
Maximum Amount of Future Payments	1,777,237
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,604,367
Expires After One Year	61,330
Total Amount Outstanding	1,665,697
Maximum Amount of Future Payments	1,665,697
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	93,671
Expires After One Year	8,473
Total Amount Outstanding	102,144
Maximum Amount of Future Payments	102,144
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	9,396
Expires After One Year	0
Total Amount Outstanding	9,396
Maximum Amount of Future Payments	$ 9,396