Supplemental Financial Information - Statement of Operations (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Operating revenues [Abstract]
Total operating revenues	$ 6,565,000,000		$ 5,254,000,000		$ 17,205,000,000		$ 14,705,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	290,000,000		207,000,000		737,000,000		602,000,000
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(69,000,000)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	33,000,000	[1]	16,000,000	[1]	143,000,000	[1]	97,000,000	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	10,000,000	[1]	13,000,000	[1]	77,000,000	[1]	39,000,000	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	202,000,000		(363,000,000)		352,000,000		(223,000,000)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	71,000,000		(141,000,000)		101,000,000		(88,000,000)
Net unrealized income (losses) on pledged assets	22,000,000		(4,000,000)		60,000,000		41,000,000
Regulatory offset to decommissioning trust fund-related activities	(208,000,000)	[2]	281,000,000	[2]	(453,000,000)	[2]	60,000,000	[2]
Total decommissioning-related activities	130,000,000		(198,000,000)		280,000,000		(74,000,000)
Investment income	5,000,000		1,000,000		15,000,000		3,000,000
Long-term lease income	7,000,000		7,000,000		22,000,000		21,000,000
Interest income related to uncertain income tax positions	0		7,000,000		14,000,000		53,000,000
Credit facility termination fees	(43,000,000)				(85,000,000)
AFUDC - equity	4,000,000		4,000,000		11,000,000		14,000,000
Bargain purchase gain related to Wolf Hollow acquisition			36,000,000				36,000,000
Other	(2,000,000)		1,000,000		(4,000,000)		1,000,000
Other, net	101,000,000		(142,000,000)		253,000,000		54,000,000
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	4,017,000,000		2,821,000,000		10,509,000,000		7,919,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	109,000,000		67,000,000		272,000,000		199,000,000
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(69,000,000)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	33,000,000	[1]	16,000,000	[1]	143,000,000	[1]	97,000,000	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	10,000,000	[1]	13,000,000	[1]	77,000,000	[1]	39,000,000	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	202,000,000		(363,000,000)		352,000,000		(223,000,000)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	71,000,000		(141,000,000)		101,000,000		(88,000,000)
Net unrealized income (losses) on pledged assets	22,000,000		(4,000,000)		60,000,000		41,000,000
Regulatory offset to decommissioning trust fund-related activities	(208,000,000)	[2]	281,000,000	[2]	(453,000,000)	[2]	60,000,000	[2]
Total decommissioning-related activities	130,000,000		(198,000,000)		280,000,000		(74,000,000)
Investment income	1,000,000		0		2,000,000		0
Interest income related to uncertain income tax positions	1,000,000		0		1,000,000		33,000,000
Credit facility termination fees	(43,000,000)				(85,000,000)
AFUDC - equity	0				0
Bargain purchase gain related to Wolf Hollow acquisition			36,000,000				36,000,000
Other	(6,000,000)		(2,000,000)		(13,000,000)		(7,000,000)
Other, net	83,000,000		(164,000,000)		185,000,000		(12,000,000)
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,484,000,000		1,784,000,000		4,154,000,000		4,694,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	81,000,000		78,000,000		224,000,000		226,000,000
Decommissioning-Related Activities [Abstract]
Investment income	0		0		1,000,000		0
Interest income related to uncertain income tax positions	1,000,000		12,000,000		1,000,000		13,000,000
AFUDC - equity	1,000,000		2,000,000		2,000,000		6,000,000
Other	3,000,000		2,000,000		8,000,000		5,000,000
Other, net	5,000,000		16,000,000		12,000,000		24,000,000
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	806,000,000		946,000,000		2,396,000,000		2,942,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	48,000,000		59,000,000		122,000,000		165,000,000
Decommissioning-Related Activities [Abstract]
Investment income	0		1,000,000		2,000,000		3,000,000
Interest income related to uncertain income tax positions	0		0		0		1,000,000
AFUDC - equity	1,000,000		2,000,000		3,000,000		8,000,000
Other	1,000,000		0		1,000,000		(1,000,000)
Other, net	2,000,000		3,000,000		6,000,000		11,000,000
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	720,000,000		745,000,000		2,032,000,000		2,394,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	48,000,000		47,000,000		143,000,000		143,000,000
Decommissioning-Related Activities [Abstract]
Investment income	3,000,000		3,000,000		9,000,000		10,000,000
Interest income related to uncertain income tax positions	0		0		0		0
AFUDC - equity	2,000,000		4,000,000		8,000,000		11,000,000
Other	0		1,000,000		1,000,000		1,000,000
Other, net	$ 5,000,000		$ 8,000,000		$ 18,000,000		$ 22,000,000

[1] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[2] Includes the elimination of NDT fund-related activity for the Regulatory Agreement Units, including the elimination of net realized income taxes related to all NDT fund activity for those units. See Note 12 of the Exelon 2011 Form 10-K for additional information regarding the accounting for nuclear decommissioning.