Commitments And Contingent Liabilities (Face Value Of Outstanding Guarantees, Current Exposure And Margin Positions) (Detail) - Power [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Face Value of Outstanding Guarantees	$ 1,772	$ 1,701
Exposure under Current Guarantees	198	153
Letters of Credit Margin Posted	115	103
Letters of Credit Margin Received	26	32
Counterparty Cash Margin Deposited	0	0
Counterparty Cash Margin Received	(10)	(1)
Net Broker Balance Deposited (Received)	403	147
Other Letters of Credit	$ 52	$ 61