Supplemental Financial Information - Statement of Operations (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Operating revenues [Abstract]
Total operating revenues	$ 5,954,000,000		$ 4,496,000,000		$ 10,640,000,000		$ 9,451,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	254,000,000		191,000,000		448,000,000		394,000,000
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(79,000,000)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	50,000,000	[1]	38,000,000	[1]	110,000,000	[1]	81,000,000	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	19,000,000	[1]	16,000,000	[1]	67,000,000	[1]	26,000,000	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(97,000,000)		28,000,000		150,000,000		140,000,000
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(35,000,000)		11,000,000		30,000,000		54,000,000
Net unrealized income (losses) on pledged assets	4,000,000		22,000,000		38,000,000		45,000,000
Regulatory offset to decommissioning trust fund-related activities	31,000,000	[2]	(70,000,000)	[2]	(245,000,000)	[2]	(221,000,000)	[2]
Total decommissioning-related activities	(28,000,000)		45,000,000		150,000,000		125,000,000
Investment income	6,000,000		1,000,000		10,000,000		2,000,000
Long-term lease income	7,000,000		7,000,000		15,000,000		14,000,000
Interest income related to uncertain income tax positions	14,000,000		43,000,000		14,000,000		46,000,000
Credit facility termination fees	(42,000,000)				(42,000,000)
AFUDC - equity	3,000,000		4,000,000		7,000,000		9,000,000
Other	(3,000,000)		1,000,000		(2,000,000)		0
Other, net	(43,000,000)		101,000,000		152,000,000		196,000,000
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	3,753,000,000		2,455,000,000		6,492,000,000		5,098,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	90,000,000		66,000,000		164,000,000		132,000,000
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(79,000,000)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	50,000,000	[1]	38,000,000	[1]	110,000,000	[1]	81,000,000	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	19,000,000	[1]	16,000,000	[1]	67,000,000	[1]	26,000,000	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(97,000,000)		28,000,000		150,000,000		140,000,000
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(35,000,000)		11,000,000		30,000,000		54,000,000
Net unrealized income (losses) on pledged assets	4,000,000		22,000,000		38,000,000		45,000,000
Regulatory offset to decommissioning trust fund-related activities	31,000,000	[2]	(70,000,000)	[2]	(245,000,000)	[2]	(221,000,000)	[2]
Total decommissioning-related activities	(28,000,000)		45,000,000		150,000,000		125,000,000
Investment income	1,000,000		0		0		0
Interest income related to uncertain income tax positions	0		33,000,000		0		33,000,000
Credit facility termination fees	(42,000,000)				(42,000,000)
AFUDC - equity	0				0
Other	(7,000,000)		(2,000,000)		(5,000,000)		(6,000,000)
Other, net	(76,000,000)		76,000,000		103,000,000		152,000,000
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,281,000,000		1,444,000,000		2,670,000,000		2,910,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	69,000,000		70,000,000		144,000,000		147,000,000
Decommissioning-Related Activities [Abstract]
Investment income	0		0		1,000,000		0
Interest income related to uncertain income tax positions	1,000,000		1,000,000		0		1,000,000
AFUDC - equity	0		2,000,000		0		4,000,000
Other	2,000,000		1,000,000		6,000,000		3,000,000
Other, net	3,000,000		4,000,000		7,000,000		8,000,000
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	715,000,000		842,000,000		1,590,000,000		1,996,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	42,000,000		51,000,000		74,000,000		106,000,000
Decommissioning-Related Activities [Abstract]
Investment income	1,000,000		1,000,000		2,000,000		2,000,000
Interest income related to uncertain income tax positions	0		0		0		1,000,000
AFUDC - equity	1,000,000		2,000,000		2,000,000		6,000,000
Other	0		0		1,000,000		(1,000,000)
Other, net	2,000,000		3,000,000		5,000,000		8,000,000
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	616,000,000		674,000,000		1,312,000,000		1,650,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	47,000,000		46,000,000		95,000,000		96,000,000
Decommissioning-Related Activities [Abstract]
Investment income	3,000,000		3,000,000		6,000,000		7,000,000
Interest income related to uncertain income tax positions	0		0		0		0
AFUDC - equity	3,000,000		3,000,000		6,000,000		7,000,000
Other	1,000,000		0		1,000,000		(1,000,000)
Other, net	$ 7,000,000		$ 6,000,000		$ 13,000,000		$ 13,000,000

[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.