Derivative Instruments and Hedging Activities - Effect of Derivative Financial Instruments on Income Statement (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest Rate Swap | Non-interest income - other
Derivative [Line Items]
Derivative financial instrument, net	$ 0	$ 0	$ 1
Interest Rate Lock Commitments | Mortgage banking operations
Derivative [Line Items]
Derivative financial instrument, net	0	0	0
Forward Delivery Commitments | Mortgage banking operations
Derivative [Line Items]
Derivative financial instrument, net	(2)	(1)	1
Credit Risk Contracts | Non-interest income - other
Derivative [Line Items]
Derivative financial instrument, net	$ 0	$ 0	$ 0