Loans and Leases - Certain Information Relating to Commercial Real Estate Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Commercial construction, acquisition and development loans	$ 1,275	$ 1,152
Credit concentration risk | Commercial construction loans
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	5.50%	5.20%
Loan portfolio diversification risk | Commercial real estate loans | Percent owner-occupied
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	30.60%	35.10%
Loan portfolio diversification risk | Commercial real estate loans | Percent non-owner-occupied
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	69.40%	64.90%