Other Income (Expense), Net (Components of Other Income (Expense), Net) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Operating revenue from contracts with customers	$ 0	$ 2	$ 1	$ 3
Other income	4	2	7	6
Other expense	(3)	(15)	(5)	(25)
Allowance for equity funds used during construction	1	2	2	2
Other income (expense), net	$ 2	$ (9)	$ 5	$ (14)