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, 2016	Dec. 31, 2015
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,257,696	$ 1,312,734
Variable interest rate commitments	13,091,598	12,822,461
Total loan commitments available for funding	14,349,294	14,135,195
Commercial and standby letters of credit	1,530,904	1,479,164
Total unfunded credit commitments	15,880,198	15,614,359
Commitments unavailable for funding	1,975,551	2,026,532
Maximum lending limits for accounts receivable factoring arrangements	960,071	1,006,404
Reserve for unfunded credit commitments	$ 34,541	$ 34,415