Investment in Constellation Energy Nuclear Group, LLC (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended				3 Months Ended		7 Months Ended	9 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended					3 Months Ended		7 Months Ended	9 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013 Power Purchase Agreement [Member]	Jun. 30, 2012 Power Purchase Agreement [Member]	Sep. 30, 2012 Power Purchase Agreement [Member]	Sep. 30, 2013 Power Purchase Agreement [Member]	Sep. 30, 2013 Power Service Agency Agreement [Member]	Jun. 30, 2012 Power Service Agency Agreement [Member]	Sep. 30, 2012 Power Service Agency Agreement [Member]	Sep. 30, 2013 Power Service Agency Agreement [Member]	Sep. 30, 2013 Administrative Services Agreement [Member]	Jun. 30, 2012 Administrative Services Agreement [Member]	Sep. 30, 2012 Administrative Services Agreement [Member]	Sep. 30, 2013 Administrative Services Agreement [Member]	Sep. 30, 2013 CENG [Member]	Sep. 30, 2012 CENG [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Minimum [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] CENG [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] CENG [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)																			50.01%		50.01%
CENG																	$ 93	$ 53																				$ 68	$ 58
Amortization of basis difference in CENG																	(88)	(131)																				(31)	(57)
Total equity investment earnings (losses) - CENG																	5	(78)																				37	1
Basis difference in investment in CENG																			204		204
Related Party Transaction [Line Items]
Required purchases of power from CENG's nuclear plants not sold to third parties (as a percent)																									85.00%
Purchase of nuclear output by EDF (as a percent)																					49.99%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings					(269)	(282)	(541)	(748)	1	1	2	3	10	14	30	32			384	473	1,129		1,263			(269)	(282)	(541)	(748)	1	1	2	3	10	14	30	32
Amount receivable from (payable to) related to agreements with CENG					(76)		(86)	(76)					4		5	4										(76)		(86)	(76)					4		5	4
Amortization of energy contract assets and liabilities	342	[1]	731	[1]																	398	[1]	812	[1]
Loan to CENG/Distribution to EDF/ Repayment to Generation																			$ 400		$ 400
Interest rate on loan to CENG																			5.25%		5.25%
Return on distributions (CENG)																			8.50%		8.50%

[1] Included in purchased power and fuel expense on the Registrants' Consolidated Statements of Operations and Comprehensive Income