Financial Risk Management Activities (Schedule Providing Credit Risk From Others, Net Of Collateral) (Detail) - Power [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Counterparty
Derivative [Line Items]
Current Exposure	$ 332
Collateral held from counterparties	26
Net Credit Exposure With Counterparties After Applying Collateral	306
Number of Counterparties greater than 10%	1
Net Exposure of Counterparties greater than 10%	$ 204
Number of active counterparties on credit risk derivatives | Counterparty	152
Investment Grade External Rating [Member]
Derivative [Line Items]
Credit exposure, percentage	99.00%
Investment Grade [Member]
Derivative [Line Items]
Current Exposure	$ 329
Collateral held from counterparties	25
Net Credit Exposure With Counterparties After Applying Collateral	304
Number of Counterparties greater than 10%	1
Net Exposure of Counterparties greater than 10%	204	[1]
Non-Investment Grade [Member]
Derivative [Line Items]
Current Exposure	3
Collateral held from counterparties	1
Net Credit Exposure With Counterparties After Applying Collateral	2
Number of Counterparties greater than 10%	0
Net Exposure of Counterparties greater than 10%	0
Cash [Member]
Derivative [Line Items]
Collateral held from counterparties	1
Letter of Credit [Member]
Derivative [Line Items]
Collateral held from counterparties	$ 25

[1] Represents net exposure with PSE&G.