Off-Balance Sheet Arrangements, Guarantees and Other Commitments Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,635,764
Expires After One Year	60,092
Total Amount Outstanding	1,695,856	$ 1,479,164
Maximum Amount of Future Payments	1,695,856
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,547,011
Expires After One Year	47,134
Total Amount Outstanding	1,594,145
Maximum Amount of Future Payments	1,594,145
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	82,544
Expires After One Year	12,958
Total Amount Outstanding	95,502
Maximum Amount of Future Payments	95,502
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	6,209
Expires After One Year	0
Total Amount Outstanding	6,209
Maximum Amount of Future Payments	$ 6,209