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, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Fixed interest rate commitments	$ 1,456,230		$ 1,475,179
Variable interest rate commitments	13,553,340		13,572,161
Total loan commitments available for funding	15,009,570		15,047,340
Commercial and standby letters of credit	1,777,237		1,695,856
Total unfunded credit commitments	16,786,807		16,743,196
Commitments unavailable for funding	1,999,306		1,719,524
Maximum lending limits for accounts receivable factoring arrangements	773,742		725,395
Reserve For Unfunded Credit Commitments	$ 47,000	$ 46,335	$ 45,265	$ 34,889	$ 34,541	$ 34,415