Notional Amount of Off-Balance Sheet Financial Instruments (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Commitments to extend credit for loans (excluding credit card loans) [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	$ 6,689,467	$ 6,471,404
Commitments to extend credit under credit card loans [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	2,975,507	2,798,433
Commercial letters of credit [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	813	1,098
Standby letters of credit [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	316,054	376,617
Forward contracts [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	29,007	49,352
Spot foreign exchange contracts [Member]
Commitments and Contingencies Disclosure [Line Items]
Contract or notional amount of off-balance sheet financial instruments	$ 628	$ 3,725