Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) MW
Powerton Station Units 5 And 6 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	IL
Lease Receivable, Gross Investment | $	$ 132
Lease Receivable, % Owned	64.00%
Lease Receivable, Total, MW | MW	1,538
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	BB-
Lease Receivable, Counterparty	NRG Energy, Inc.
Joliet Station Units 7 And 8 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	IL
Lease Receivable, Gross Investment | $	$ 85
Lease Receivable, % Owned	64.00%
Lease Receivable, Total, MW | MW	1,036
Lease Receivable, Asset, Fuel Type	Gas
Lease Receivable, Counterparties' S&P Credit Ratings	BB-
Lease Receivable, Counterparty	NRG Energy, Inc.
Keystone Station Units 1 And 2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment | $	$ 20
Lease Receivable, % Owned	17.00%
Lease Receivable, Total, MW | MW	1,711
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	CCC-
Lease Receivable, Counterparty	REMA (A)	[1]
Conemaugh Station Units 1 And 2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment | $	$ 20
Lease Receivable, % Owned	17.00%
Lease Receivable, Total, MW | MW	1,711
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	CCC-
Lease Receivable, Counterparty	REMA (A)	[1]
Shawville Station Units 1, 2, 3 And 4 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment | $	$ 78
Lease Receivable, % Owned	100.00%
Lease Receivable, Total, MW | MW	596
Lease Receivable, Asset, Fuel Type	Gas
Lease Receivable, Counterparties' S&P Credit Ratings	CCC-
Lease Receivable, Counterparty	REMA (A)	[1]

[1] GenOn Energy Inc. (GenOn), and certain of its subsidiaries (which did not include REMA) filed voluntary petitions for relief under Chapter 11 of the U.S. Bankruptcy Code. GenOn is currently engaged in a balance sheet restructuring, which will take an undetermined time to complete. Certain subsidiaries of Energy Holdings, REMA, consenting holders of the pass-through certificates and other parties entered into a Forbearance relating to the Conemaugh facility. For additional information, see Note 7. Long-Term Investments.