Other Income (Expense), Net (Components of Other Income (Expense), Net) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Operating revenue from contracts with customers	$ 0	$ 1	$ 1	$ 4
Other income	3	11	10	17
Other expense	(6)	(23)	(11)	(48)
Allowance for equity funds used during construction	1	(2)	3	0
Other income (expense), net	$ (2)	$ (13)	$ 3	$ (27)