Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) MW
Powerton Station Units 5 And 6 [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	IL
Lease Receivable, Gross Investment | $	$ 75
Lease Receivable, % Owned	64.00%
Lease Receivable, Total, MW | MW	1,538
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, Counterparties' S&P Credit Ratings	BB
Lease Receivable, Counterparty	NRG Energy, Inc.
Shawville Station [Member]
Financing Receivable, Recorded Investment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment | $	$ 75
Lease Receivable, % Owned	100.00%
Lease Receivable, Total, MW | MW	596
Lease Receivable, Counterparties' S&P Credit Ratings	NR
Lease Receivable, Counterparty	REMA (A)	[1]

[1] REMA emerged from Chapter 11 of the U.S. Bankruptcy Code in December 2018. For additional information, see Note 9. Long-Term Investments.