Investment in Constellation Energy Nuclear Group, LLC (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended				3 Months Ended			6 Months Ended	3 Months Ended			6 Months Ended	3 Months Ended			6 Months Ended			3 Months Ended		6 Months Ended					3 Months Ended			6 Months Ended	3 Months Ended			6 Months Ended	3 Months Ended			6 Months Ended	3 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013 Power Purchase Agreement [Member]	Jun. 30, 2012 Power Purchase Agreement [Member]	Jun. 30, 2012 Power Purchase Agreement [Member]	Jun. 30, 2013 Power Purchase Agreement [Member]	Jun. 30, 2013 Power Service Agency Agreement [Member]	Jun. 30, 2012 Power Service Agency Agreement [Member]	Jun. 30, 2012 Power Service Agency Agreement [Member]	Jun. 30, 2013 Power Service Agency Agreement [Member]	Jun. 30, 2013 Administrative Services Agreement [Member]	Jun. 30, 2012 Administrative Services Agreement [Member]	Jun. 30, 2012 Administrative Services Agreement [Member]	Jun. 30, 2013 Administrative Services Agreement [Member]	Jun. 30, 2013 CENG [Member]	Jun. 30, 2012 CENG [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member]		Jun. 30, 2013 Exelon Generation Co L L C [Member] Minimum [Member]	Jun. 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]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Jun. 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]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Jun. 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]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member] CENG [Member]	Jun. 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																	$ 26	$ (5)																				$ 11	$ 4
Amortization of basis difference in CENG																	(57)	(74)																				(30)	(62)
Total equity investment earnings (losses) - CENG																	(31)	(79)																				(19)	(58)
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					(231)	(216)	(251)	(479)	1	2	2	2	11	12	15	22			352	420	744		790			(231)	(216)	(251)	(479)	1	2	2	2	11	12	15	22
Amount receivable from (payable to) related to agreements with CENG					(91)	(90)	(90)	(91)					4	4	4	4										(91)	(90)	(90)	(91)					4	4	4	4
Amortization of energy contract assets and liabilities	306	[1]	485	[1]																	344	[1]	532	[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