Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,500,316
Expires After One Year	30,588
Total Amount Outstanding	1,530,904	$ 1,479,164
Maximum Amount of Future Payments	1,530,904
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,421,632
Expires After One Year	25,365
Total Amount Outstanding	1,446,997
Maximum Amount of Future Payments	1,446,997
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	67,298
Expires After One Year	5,223
Total Amount Outstanding	72,521
Maximum Amount of Future Payments	72,521
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	11,386
Expires After One Year	0
Total Amount Outstanding	11,386
Maximum Amount of Future Payments	$ 11,386