Related Party Transactions (Details) (USD $)	3 Months Ended					1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended						3 Months Ended		1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended						3 Months Ended			3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012	Mar. 31, 2012 Power Purchase Agreement [Member]	Mar. 31, 2013 Power Purchase Agreement [Member]	Mar. 31, 2012 Power Service Agency Agreement [Member]	Mar. 31, 2013 Power Service Agency Agreement [Member]	Mar. 31, 2012 Administrative Services Agreement [Member]	Mar. 31, 2013 Administrative Services Agreement [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Minimum [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Maximum [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Power Purchase Agreement [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Power Service Agency Agreement [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Administrative Services Agreement [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] CENG [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] CENG [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Mar. 31, 2013 PECO Energy Co [Member]	Mar. 31, 2012 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member]	Mar. 31, 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%
CENG																									$ 15,000,000	$ (9,000,000)
Amortization of basis difference in CENG																									(27,000,000)	(12,000,000)
Total equity investment earnings (losses) - CENG																									(12,000,000)	(21,000,000)
Basis difference in investment in CENG												204,000,000
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates						(35,000,000)	(248,000,000)	1,000,000	1,000,000	3,000,000	11,000,000	392,000,000		370,000,000					(35,000,000)	(248,000,000)	1,000,000	1,000,000	3,000,000	11,000,000			1,000,000	1,000,000		0	1,000,000		4,000,000	3,000,000
Purchased power from affiliate	0		0									0															145,000,000	247,000,000		141,000,000	111,000,000		113,000,000	92,000,000
Operating and maintenance from affiliate												147,000,000		140,000,000													36,000,000	42,000,000		24,000,000	30,000,000		19,000,000	42,000,000
Total interest expense to affiliates, net	6,000,000		6,000,000																								3,000,000	3,000,000		3,000,000	3,000,000
Total income (loss) in equity method investments	(9,000,000)		(22,000,000)									(9,000,000)		(22,000,000)
Cash distribution paid to member												211,000,000		600,000,000
Cash dividends paid to parent	450,000,000		350,000,000																								55,000,000	75,000,000		83,000,000	87,000,000		0	0
Contributions from parent																											0	0		0	0		0
Contributions from member												0		0
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates												85,000,000				226,000,000
Total receivables from affiliates (current)												132,000,000				141,000,000
Total receivable from affiliates (noncurrent)																											2,314,000,000		2,039,000,000	392,000,000		360,000,000
Investments in affiliates	22,000,000				22,000,000							0				0											6,000,000		6,000,000	8,000,000		8,000,000	8,000,000		8,000,000
Total payables to affiliates (current)												165,000,000				193,000,000											68,000,000		97,000,000	76,000,000		76,000,000	45,000,000		65,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)																											85,000,000		226,000,000
Total payables to affiliates (noncurrent)												2,531,000,000				2,397,000,000
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%	90.00%
Purchase of nuclear output by EDF (as a percent)												49.99%
Maximum cost of service per month												280,000
Impact Of Transactions Under Agreements [Abstract]
Amount receivable from (payable to) related to agreements with CENG							(70,000,000)		0		4,000,000									(70,000,000)		0		4,000,000
Amortization of energy contract assets and liabilities	$ 176,000,000	[1]	$ 131,000,000	[1]								$ 176,000,000	[1]	$ 131,000,000	[1]

[1] Included in revenues or fuel expense on the Registrants' Consolidated Statements of Operations and Comprehensive Income.