Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 MW
Powerton Station Units 5 And 6 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	IL
Lease Receivable, Gross Investment	$ 134
Lease Receivable Percent Owned	64.00%
Lease Receivable, Total, 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]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	IL
Lease Receivable, Gross Investment	84
Lease Receivable Percent Owned	64.00%
Lease Receivable, Total, MW	1,044
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	BB-
Lease Receivable, Counterparty	NRG Energy, Inc.
Keystone Station Units 1 And 2 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment	121
Lease Receivable Percent Owned	17.00%
Lease Receivable, Total, MW	1,711
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	NRG REMA LLC
Conemaugh Station Units 1 And 2 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment	121
Lease Receivable Percent Owned	17.00%
Lease Receivable, Total, MW	1,711
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	NRG REMA LLC
Shawville Station Units 1, 2, 3 And 4 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment	$ 113
Lease Receivable Percent Owned	100.00%
Lease Receivable, Total, MW	603
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	NRG REMA LLC