Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2017 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 | MW	1,538
Fuel Type	Coal
Counterparties’ S&P Credit Ratings	BB-
Counterparty	NRG Energy, Inc.
Joliet Station Units 7 And 8 [Member]
Schedule of Financial Receivables [Line Items]
Location	IL
Gross Investment | $	$ 83
% Owned	64.00%
Total MW | MW	1,036
Fuel Type	Gas
Counterparties’ S&P Credit Ratings	BB-
Counterparty	NRG Energy, Inc.
Keystone Station Units 1 And 2 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment | $	$ 20
% Owned	17.00%
Total MW | MW	1,711
Fuel Type	Coal
Counterparties’ S&P Credit Ratings	CC (A)	[1]
Counterparty	REMA
Conemaugh Station Units 1 And 2 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment | $	$ 20
% Owned	17.00%
Total MW | MW	1,711
Fuel Type	Coal
Counterparties’ S&P Credit Ratings	CC (A)	[1]
Counterparty	REMA
Shawville Station Units 1, 2, 3 And 4 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment | $	$ 91
% Owned	100.00%
Total MW | MW	596
Fuel Type	Gas
Counterparties’ S&P Credit Ratings	CC (A)	[1]
Counterparty	REMA

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