Employee Benefit Plans and Equity Compensation Plan (Schedule of Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss	$ 2	$ (1)	$ 1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss	$ (2)	$ 1	$ (1)