Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 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, % Owned	64.00%
Lease Receivable, Total, MW	0
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	CCC
Lease Receivable, Counterparty	Edison Mission Energy
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, % Owned	64.00%
Lease Receivable, Total, MW	0
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	CCC
Lease Receivable, Counterparty	Edison Mission Energy
Keystone Station Units 1 And 2 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment	114
Lease Receivable, % Owned	17.00%
Lease Receivable, Total, MW	0
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	GenOn REMA, LLC
Conemaugh Station Units 1 And 2 [Member]
Property, Plant and Equipment [Line Items]
Lease Receivable, Asset Location	PA
Lease Receivable, Gross Investment	114
Lease Receivable, % Owned	17.00%
Lease Receivable, Total, MW	0
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	GenOn 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	$ 109
Lease Receivable, % Owned	100.00%
Lease Receivable, Total, MW	0
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B-
Lease Receivable, Counterparty	GenOn REMA, LLC