Commitments And Contingent Liabilities (Guaranteed Obligations) (Detail) - Power [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Face Value of Outstanding Guarantees	$ 1,797	$ 1,734
Exposure under Current Guarantees	143	172
Letters of Credit Margin Posted	164	122
Letters of Credit Margin Received	136	192
Counterparty Cash Margin Deposited	0	0
Counterparty Cash Margin Received	(4)	(15)
Net Broker Balance Deposited (Received)	(12)	(5)
Other Letters of Credit	51	$ 51
PennEast Natural Gas Pipeline [Member]
Loss Contingencies [Line Items]
Face Value of Outstanding Guarantees	106
755 MW Gas-Fired Combined Cycle Generating Station [Member]
Loss Contingencies [Line Items]
Face Value of Outstanding Guarantees	$ 21