Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) MW
Powerton Station Units 5 And 6 [Member]
Schedule of Financial Receivables [Line Items]
Location	IL
Gross Investment	$ 134
% Owned	64.00%
Total | MW	1,538
Fuel Type	Coal
Counter-parties’ S&P Credit Ratings As of September 30, 2015 (A)	BB-
Counterparty	NRG Energy, Inc.
Joliet Station Units 7 And 8 [Member]
Schedule of Financial Receivables [Line Items]
Location	IL
Gross Investment	$ 84
% Owned	64.00%
Total | MW	1,044
Fuel Type	Coal
Counter-parties’ S&P Credit Ratings As of September 30, 2015 (A)	BB-
Counterparty	NRG Energy, Inc.
Keystone Station Units 1 And 2 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment	$ 121
% Owned	17.00%
Total | MW	1,711
Fuel Type	Coal
Counter-parties’ S&P Credit Ratings As of September 30, 2015 (A)	B-
Counterparty	NRG REMA, LLC
Conemaugh Station Units 1 And 2 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment	$ 121
% Owned	17.00%
Total | MW	1,711
Fuel Type	Coal
Counter-parties’ S&P Credit Ratings As of September 30, 2015 (A)	B-
Counterparty	NRG REMA, LLC
Shawville Station Units 1, 2, 3 And 4 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment	$ 113
% Owned	100.00%
Total | MW	603
Fuel Type	Coal
Counter-parties’ S&P Credit Ratings As of September 30, 2015 (A)	B-
Counterparty	NRG REMA, LLC