Commitments and Contingencies - Commitments and Contingent Liabilities Outstanding (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commitments to extend credit
Home equity lines of credit	$ 5,451,328	$ 5,484,197
Commercial real estate loans to be sold	393,397	229,401
Other commercial real estate	8,222,395	7,556,722
Residential real estate loans to be sold	530,093	245,211
Other residential real estate	511,854	219,351
Commercial and other	16,313,801	14,363,803
Standby letters of credit	2,373,846	2,326,991
Commercial letters of credit	38,633	55,808
Financial guarantees and indemnification contracts	3,996,029	3,529,136
Commitments to sell real estate loans	$ 1,350,292	$ 940,692