Segment Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Total revenues	$ 4,686,000,000	[1]	$ 4,956,000,000	[1]
Intersegment revenues	0	[2]	1,000,000	[2]
Income taxes	158,000,000		446,000,000
Net income (loss)	200,000,000		669,000,000
Total assets	77,628,000,000				54,995,000,000
Amount of revenue from transactions with other operating segments of the same entity.	0	[2]	1,000,000	[2]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	0	[2]	1,000,000	[2]
Segment Reporting Additional Narrative Information [Abstract]
Unrealized Gain (Loss) on ComEd Swap (Generation Intersegment Revenues)	11,000,000
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Total revenues	2,739,000,000	[1],[3]	2,643,000,000	[1],[3]
Intersegment revenues	366,000,000	[2],[3]	306,000,000	[2],[3]
Net income (loss)	166,000,000	[3]	495,000,000	[3]
Total assets	41,723,000,000	[3]			27,433,000,000	[3]
Revenues from external customers for Generation	2,739,000,000	[4]	2,643,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	366,000,000	[2],[3]	306,000,000	[2],[3]
Revenues net of purchased power and fuel expense from external customers for Generation	1,695,000,000	[5]	1,760,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	0
Total revenues net of purchased power and fuel expense for Generation	1,695,000,000		1,760,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	366,000,000	[2],[3]	306,000,000	[2],[3]
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	13,000,000		6,000,000
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Total revenues	966,000,000		1,075,000,000
Intersegment revenues	(4,000,000)
Revenues from external customers for Generation	970,000,000	[4]	1,075,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	(4,000,000)
Revenues net of purchased power and fuel expense from external customers for Generation	774,000,000	[5]	914,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(4,000,000)
Total revenues net of purchased power and fuel expense for Generation	770,000,000		914,000,000
Intersegment revenues for Generation with PECO	111,000,000		143,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	(4,000,000)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Total revenues	1,219,000,000		1,427,000,000
Intersegment revenues	4,000,000
Revenues from external customers for Generation	1,215,000,000	[4]	1,427,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000
Revenues net of purchased power and fuel expense from external customers for Generation	813,000,000	[5]	965,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	4,000,000
Total revenues net of purchased power and fuel expense for Generation	817,000,000		965,000,000
Intersegment revenues for Generation with ComEd	247,000,000		163,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000
Generation New England [Member]
Segment Reporting Information [Line Items]
Total revenues	93,000,000		3,000,000
Intersegment revenues	2,000,000
Revenues from external customers for Generation	91,000,000	[4]	3,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	2,000,000
Revenues net of purchased power and fuel expense from external customers for Generation	37,000,000	[5]	2,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	2,000,000
Total revenues net of purchased power and fuel expense for Generation	39,000,000		2,000,000
Intersegment revenues for Generation with BGE	19,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	2,000,000
Generation New York [Member]
Segment Reporting Information [Line Items]
Total revenues	43,000,000		0
Intersegment revenues	(2,000,000)
Revenues from external customers for Generation	45,000,000	[4]	0	[4]
Amount of revenue from transactions with other operating segments of the same entity.	(2,000,000)
Revenues net of purchased power and fuel expense from external customers for Generation	10,000,000	[5]	0
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(2,000,000)
Total revenues net of purchased power and fuel expense for Generation	8,000,000		0
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	(2,000,000)
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Total revenues	128,000,000		101,000,000
Intersegment revenues	0
Revenues from external customers for Generation	128,000,000	[4]	101,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	0
Revenues net of purchased power and fuel expense from external customers for Generation	34,000,000	[5]	4,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	0
Total revenues net of purchased power and fuel expense for Generation	34,000,000		4,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	0
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Total revenues	79,000,000	[6]	37,000,000	[6]
Intersegment revenues	4,000,000	[6]
Revenues from external customers for Generation	75,000,000	[4],[6]	37,000,000	[4],[6]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000	[6]
Revenues net of purchased power and fuel expense from external customers for Generation	10,000,000	[5],[6]	(8,000,000)	[6]
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	4,000,000	[6]
Total revenues net of purchased power and fuel expense for Generation	14,000,000	[6]	(8,000,000)	[6]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000	[6]
Generation Reportable Segment Revenues [Member]
Segment Reporting Information [Line Items]
Total revenues	2,528,000,000		2,643,000,000
Intersegment revenues	4,000,000
Revenues from external customers for Generation	2,524,000,000	[4]	2,643,000,000	[4]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000
Revenues net of purchased power and fuel expense from external customers for Generation	1,678,000,000	[5]	1,877,000,000
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	4,000,000
Total revenues net of purchased power and fuel expense for Generation	1,682,000,000		1,877,000,000
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	4,000,000
Generation Other Activity [Member]
Segment Reporting Information [Line Items]
Total revenues	211,000,000	[7]	0	[7]
Intersegment revenues	(4,000,000)	[7]
Revenues from external customers for Generation	215,000,000	[4],[7]	0	[4],[7]
Amount of revenue from transactions with other operating segments of the same entity.	(4,000,000)	[7]
Revenues net of purchased power and fuel expense from external customers for Generation	17,000,000	[5],[7]	(117,000,000)	[7]
Amount of revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(4,000,000)	[7]
Total revenues net of purchased power and fuel expense for Generation	13,000,000	[7]	(117,000,000)	[7]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	(4,000,000)	[7]
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Total revenues	1,388,000,000	[1]	1,466,000,000	[1]
Intersegment revenues	1,000,000	[2]	1,000,000	[2]
Net income (loss)	87,000,000		69,000,000
Total assets	22,589,000,000				22,638,000,000
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2]	1,000,000	[2]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2]	1,000,000	[2]
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	61,000,000		64,000,000
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Total revenues	875,000,000	[1]	1,153,000,000	[1]
Intersegment revenues	1,000,000	[2]	1,000,000	[2]
Net income (loss)	97,000,000		126,000,000
Total assets	9,215,000,000				9,156,000,000
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2]	1,000,000	[2]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2]	1,000,000	[2]
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	34,000,000		48,000,000
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	52,000,000	[1],[8]
Intersegment revenues	1,000,000	[2],[8]
Net income (loss)	(65,000,000)	[8]
Total assets	7,369,000,000	[8]
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2],[8]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	1,000,000	[2],[8]
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	3,000,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	351,000,000	[1],[9]	186,000,000	[1],[9]
Intersegment revenues	350,000,000	[2],[9]	186,000,000	[2],[9]
Net income (loss)	(85,000,000)	[9]	(21,000,000)	[9]
Total assets	10,876,000,000	[9]			6,162,000,000	[9]
Amount of revenue from transactions with other operating segments of the same entity.	350,000,000	[2],[9]	186,000,000	[2],[9]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	350,000,000	[2],[9]	186,000,000	[2],[9]
Business Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(719,000,000)	[1]	(492,000,000)	[1]
Intersegment revenues	(719,000,000)	[2]	(493,000,000)	[2]
Net income (loss)	0		0
Total assets	(14,144,000,000)				(10,394,000,000)
Amount of revenue from transactions with other operating segments of the same entity.	(719,000,000)	[2]	(493,000,000)	[2]
Segment Reporting Intersegment Revenue [Abstract]
Amount of revenue from transactions with other operating segments of the same entity.	$ (719,000,000)	[2]	$ (493,000,000)	[2]

[1] For the three months ended March 31, 2012 and 2011, utility taxes of $ 13 million and $ 6 million, respectively, are included in revenues and expenses for Generation. For the three months ended March 31, 2012 and 2011, utility taxes of $61 million and $64 million, respectively, are included in revenues and expenses for ComEd. For the three months ended March 31, 2012 and 2011, utility taxes of $34 million and $48 million, respectively, are included in revenues and expenses for PECO. For the period of March 12, 2012 through March 31, 2012, utility taxes of $3 million are included in revenues and expenses for BGE.

[2] The intersegment profit associated with Generation's sale of AECs to PECO is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. See Note 2 of the Exelon 2011 Form 10-K for additional information on AECs. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations.

[3] Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Regions. Intersegment revenues for Generation for the three months ended March 31, 2012 include revenue from sales to PECO of $111 million and sales to BGE of $19 million in the Mid-Atlantic region, and sales to ComEd of $247 million in the Midwest region, net of $11 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the three months ended March 31, 2011 intersegment revenues for Generation include revenue from sales to PECO of $143 million in the Mid-Atlantic region, and sales to ComEd of $163 million in the Midwest region.

[4] Includes all wholesale and retail electric sales from third parties and affiliated sales to ComEd, PECO and BGE.

[5] Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE.

[6] Other regions includes the South, West and Canada, which are not considered individually significant.

[7] Other represents activities not allocated to a region and includes retail and wholesale gas, upstream natural gas, proprietary trading, demand response, energy efficiency, the design, construction, and operation of renewable energy, heating, cooling, and cogeneration facilities, home improvements, sales of electric and gas appliances, servicing of heating, air conditioning, plumbing, electrical, and indoor quality systems, mark-to-market activities associated with Generation's economic hedging activities. In addition, includes generation under the reliability-must-run rate schedule and generation of Brandon Shores, H.A. Wagner, and C.P. Crane, the generating facilities planned for divestiture as a result of the Exelon and Constellation merger. Also includes amortization of intangible assets related to commodity contracts recorded at fair value at the merger date.

[8] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through March 31, 2012.

[9] Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.