Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	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		9 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				9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 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]		Dec. 31, 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]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Sep. 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																				$ 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 Income Statement Activity [Abstract]
Operating revenues from affiliates								(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			1	0	2	2		1	1	1	3		2	4	10	9
Purchased power from affiliate																																												143	180	409	631		82	171	321	407
Operating and maintenance from affiliate																						140	140	434		467																		37	37	113	118		24	27	74	83		21	29	59	97
Total interest expense to affiliates, net	6	6	19		19																																							3	3	10	9		3	3	9	9
Total income (loss) in equity method investments			7		(69)																			7		(69)
Cash distribution paid to member																								550		1,384
Cash dividends paid to parent			981		1,226																																									165	95				248	258				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																						0		0				226
Total receivables from affiliates (current)																						107		107				141
Total receivable from affiliates (noncurrent)																																												2,361		2,361		2,039	410		410		360
Investments in affiliates	23		23				22															0		0				0																6		6		6	8		8		8	8		8		8
Total payables to affiliates (current)																						162		162				193																61		61		97	51		51		76	54		54		65
Mark-to-market derivative liabilities with affiliate (current liabilities)																																												0		0		226
Total payables to affiliates (noncurrent)																						2,593		2,593				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								(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]

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