Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	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					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
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 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]		Dec. 31, 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]	Jun. 30, 2013 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2013 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2013 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2013 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [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 Income Statement Activity [Abstract]
Operating revenues from affiliates									(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				1	1	1			1		2		4	2	8	5
Purchased power from affiliate																																													121	203	266	451		97	125	238	235
Operating and maintenance from affiliate																							148	188	295		327																		40	38	76	81		26	26	50	57		21	25	37	59
Total interest expense to affiliates, net	6	6	13		12																																								4	3	7	6		3	3	6	6
Total income (loss) in equity method investments			(30)		(79)																				(30)		(79)
Cash distribution paid to member																									474		891
Cash dividends paid to parent			716		773																																										110	85				166	172				0	0
Contributions from parent																																															0	0									0	66
Contributions from member																									0		0
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates							(226)	[1]															0		0				226
Total receivables from affiliates (current)																							123		123				141
Total receivable from affiliates (noncurrent)																																													2,244		2,244		2,039	366		366		360
Investments in affiliates	22		22				22																0		0				0																6		6		6	8		8		8	8		8		8
Total payables to affiliates (current)																							148		148				193																70		70		97	60		60		76	59		59		65
Mark-to-market derivative liabilities with affiliate (current liabilities)																																													0		0		226
Total payables to affiliates (noncurrent)																							2,433		2,433				2,397
Equity Method Investment Summarized Financial Information[Abstract]
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]
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	[2]	$ 485	[2]																			$ 344	[2]	$ 532	[2]

[1] (a)        Includes current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $226 million related to the fair value of the five-year financial swap contract between Generation and ComEd, as described above

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