Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,674,115
Expires After One Year	52,246
Total Amount Outstanding	1,726,361	$ 1,479,164
Maximum Amount of Future Payments	1,726,361
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,589,967
Expires After One Year	41,490
Total Amount Outstanding	1,631,457
Maximum Amount of Future Payments	1,631,457
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	73,261
Expires After One Year	10,756
Total Amount Outstanding	84,017
Maximum Amount of Future Payments	84,017
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	10,887
Expires After One Year	0
Total Amount Outstanding	10,887
Maximum Amount of Future Payments	$ 10,887