Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,452,107	$ 1,475,179
Variable interest rate commitments	12,950,544	13,572,161
Total loan commitments available for funding	14,402,651	15,047,340
Commercial and standby letters of credit	1,679,680	1,695,856
Total unfunded credit commitments	16,082,331	16,743,196
Commitments unavailable for funding	1,952,726	1,719,524
Maximum lending limits for accounts receivable factoring arrangements	686,553	725,395
Reserve For Unfunded Credit Commitments	$ 46,335	$ 45,265	$ 34,541	$ 34,415