Commitments and Contingencies - Commitments and Contingent Liabilities Outstanding (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments to extend credit
Home equity lines of credit	$ 5,442,160	$ 5,484,197
Commercial real estate loans to be sold	164,076	229,401
Other commercial real estate	9,029,608	7,556,722
Residential real estate loans to be sold	423,056	245,211
Other residential real estate	448,375	219,351
Commercial and other	16,170,731	14,363,803
Standby letters of credit	2,441,432	2,326,991
Commercial letters of credit	41,059	55,808
Financial guarantees and indemnification contracts	4,108,572	3,529,136
Commitments to sell real estate loans	$ 906,037	$ 940,692