Fair Value Measurements - Additional Information about Assets Measured at Fair Value on Recurring Basis (Detail) - Fair value, measurements, recurring - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 3	$ 1
Issuances	24	3
Settlements	(3)	(1)
Balance at end of period	24	3
Interest Rate Lock Commitments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	3	1
Issuances	24	3
Settlements	(3)	(1)
Balance at end of period	$ 24	$ 3