Loans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred origination costs (fees)	$ 79	$ 77
Net unamortized premium (discount)	3	11
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	$ 289	$ 289
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Outstanding to Executive Officers and Director as Percent of Shareholders' Equity, Maximum	5.00%	5.00%