Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,302,359	$ 1,312,734
Variable interest rate commitments	12,473,768	12,822,461
Total loan commitments available for funding	13,776,127	14,135,195
Commercial and standby letters of credit	1,726,361	1,479,164
Total unfunded credit commitments	15,502,488	15,614,359
Commitments unavailable for funding	2,001,114	2,026,532
Maximum lending limits for accounts receivable factoring arrangements	878,460	1,006,404
Reserve for unfunded credit commitments	$ 34,889	$ 34,415