Commitments and Contingencies - Commitments and Contingent Liabilities Outstanding (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Commitments to extend credit
Home equity lines of credit	$ 5,489,356	$ 5,484,197
Commercial real estate loans to be sold	247,494	229,401
Other commercial real estate	7,771,353	7,556,722
Residential real estate loans to be sold	473,275	245,211
Other residential real estate	414,375	219,351
Commercial and other	15,188,645	14,363,803
Standby letters of credit	2,353,515	2,326,991
Commercial letters of credit	43,824	55,808
Financial guarantees and indemnification contracts	3,741,060	3,529,136
Commitments to sell real estate loans	$ 1,377,712	$ 940,692