Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Regulatory Liability for Excess Deferred Taxes adjustment	$ 35
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	28
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 53
Bonus Depreciation For Tax Purposes		50.00%
NJ temporary surtax 2018 to 2019	2.50%	2.50%
NJ temporary surtax 2020 to 2021	1.50%	1.50%
Minimum [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 50	$ 50
Maximum [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 120	$ 120