Commitments And Contingent Liabilities (Face Value Of Outstanding Guarantees, Current Exposure And Margin Positions) (Detail) - Power [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Commitments [Line Items]
Face Value of Outstanding Guarantees	$ 1,806	$ 1,734
Exposure under Current Guarantees	139	172
Letters of Credit Margin Posted	157	122
Letters of Credit Margin Received	99	192
Counterparty Cash Margin Deposited	0	0
Counterparty Cash Margin Received	(1)	(15)
Net Broker Balance Deposited (Received)	57	(5)
Other Letters of Credit	51	$ 51
755 MW Gas-Fired Combined Cycle Generating Station [Member]
Other Commitments [Line Items]
Face Value of Outstanding Guarantees	21
PennEast Natural Gas Pipeline [Member]
Other Commitments [Line Items]
Face Value of Outstanding Guarantees	$ 106