Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,592,167
Expires After One Year	64,345
Total Amount Outstanding	1,656,512	$ 1,479,164
Maximum Amount of Future Payments	1,656,512
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,489,185
Expires After One Year	49,744
Total Amount Outstanding	1,538,929
Maximum Amount of Future Payments	1,538,929
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	94,872
Expires After One Year	14,601
Total Amount Outstanding	109,473
Maximum Amount of Future Payments	109,473
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	8,110
Expires After One Year	0
Total Amount Outstanding	8,110
Maximum Amount of Future Payments	$ 8,110