Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 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	1,538
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	D
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	1,044
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	D
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	116
Lease Receivable, % 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	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	116
Lease Receivable, % 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	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	603
Lease Receivable, Asset, Fuel Type	Coal
Lease Receivable, Counterparties' S&P Credit Ratings	B
Lease Receivable, Counterparty	GenOn REMA, LLC