Financing Receivables (Schedule Of Assets Under Lease Receivables) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 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 | $	$ 26
% Owned	17.00%
Total MW | MW	1,711
Fuel Type	Coal
Counterparties’ S&P Credit Ratings	CCC- (A)	[1]
Counterparty	REMA
Conemaugh Station Units 1 And 2 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment | $	$ 29
% Owned	17.00%
Total MW | MW	1,711
Fuel Type	Coal
Counterparties’ S&P Credit Ratings	CCC- (A)	[1]
Counterparty	REMA
Shawville Station Units 1, 2, 3 And 4 [Member]
Schedule of Financial Receivables [Line Items]
Location	PA
Gross Investment | $	$ 99
% Owned	100.00%
Total MW | MW	596
Fuel Type	Gas
Counterparties’ S&P Credit Ratings	CCC- (A)	[1]
Counterparty	REMA

[1] REMA’s parent company, GenOn Energy Inc. (GenOn), reported in August 2016 that GenOn did not expect to have sufficient liquidity to repay its senior unsecured notes due in June 2017. In January 2017, S&P further lowered its corporate credit rating on GenOn and its affiliates (including REMA) to “CCC-” from “CCC” reflecting the primary credit concern of the near-term maturity of GenOn’s senior unsecured notes in June 2017 and expressed a negative outlook reflecting the continuing pressure on financial measures. In October 2016, Moody’s downgraded the GenOn Corporate Family Rating to “Caa3” to reflect its high debt burden relative to cash flow.