Other Income (Expense), Net (Components of Other Income (Expense), Net) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Operating revenue from contracts with customers	$ 0	$ 1
Other income	3	3
Other expense	2	(2)
Allowance for equity funds used during construction	1	1
Other income, net	$ 6	$ 3