Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,626,484
Expires After One Year	53,196
Total Amount Outstanding	1,679,680	$ 1,695,856
Maximum Amount of Future Payments	1,679,680
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,519,329
Expires After One Year	45,306
Total Amount Outstanding	1,564,635
Maximum Amount of Future Payments	1,564,635
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	89,155
Expires After One Year	7,890
Total Amount Outstanding	97,045
Maximum Amount of Future Payments	97,045
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	18,000
Expires After One Year	0
Total Amount Outstanding	18,000
Maximum Amount of Future Payments	$ 18,000