Other Income (Expense), Net (Components of Other Income (Expense), Net) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Operating revenue from contracts with customers	$ 0	$ 0	$ 0	$ 1
Other income	4	4	7	7
Other expense	(18)	(3)	(16)	(5)
Allowance for equity funds used during construction	2	1	3	2
Other income (expense), net	$ (12)	$ 2	$ (6)	$ 5