Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 ReportableSegments		Mar. 31, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	$ 6,082	[1]	$ 4,690	[1]
Revenues	6,082		4,690
Income taxes	56		158
Net income (loss)	1		200
Total assets	78,243				78,561
Segment Reporting Additional Information [Abstract]
Number of reportable segments	9
Unrealized Gain (Loss) on Derivatives	(388)		73
All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	318	[1],[2]	351	[1],[2]
Intersegment revenues	318	[2],[3],[4],[5]	346	[2],[3],[4],[5]
Net income (loss)	(103)	[2],[4]	(85)	[2],[4]
Total assets	10,139	[2]			10,432	[2]
Business Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	(704)	[1]	(719)	[1]
Intersegment revenues	(704)	[3]	(719)	[3]
Total assets	(12,273)				(12,316)
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	3,533	[1],[6]	2,743	[1],[6]
Intersegment revenues	381	[3],[6]	370	[3],[6]
Net income (loss)	(17)	[6]	166	[6]
Total assets	39,991	[6]			40,681	[6]
Segment Reporting Additional Information [Abstract]
Number of reportable segments	6
Exelon Generation Co L L C [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	21		13
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	113		19
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	145		247
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives	(17)		11
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	141		111
Generation Mid Atlantic [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,323		966
Intersegment revenues	(8)		(4)
Revenues	1,331	[7]	970
Revenue net of purchased power and fuel expense from external customers	852	[8]	774	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(8)		(4)
Revenue net of purchased power and fuel expense, Total	844		770
Generation Midwest [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,188		1,219
Intersegment revenues	7		4
Revenues	1,181	[7]	1,215
Revenue net of purchased power and fuel expense from external customers	710	[8]	813	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	7		4
Revenue net of purchased power and fuel expense, Total	717		817
Generation New England [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	403		93
Intersegment revenues	12		2
Revenues	391	[7]	91
Revenue net of purchased power and fuel expense from external customers	18	[8]	37	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	12		2
Revenue net of purchased power and fuel expense, Total	30		39
Generation New York [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	169		43
Intersegment revenues	(6)		(2)
Revenues	175	[7]	45
Revenue net of purchased power and fuel expense from external customers	(16)	[8]	10	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(6)		(2)
Revenue net of purchased power and fuel expense, Total	(22)		8
Generation ERCOT [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	293		128
Intersegment revenues	0
Revenues	293	[7]	128
Revenue net of purchased power and fuel expense from external customers	112	[8]	34	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(11)
Revenue net of purchased power and fuel expense, Total	101		34
Generation Other Regions [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	225	[9]	79	[9]
Intersegment revenues	42	[9]	4	[9]
Revenues	183	[7],[9]	75	[9]
Revenue net of purchased power and fuel expense from external customers	10	[10],[8]	10	[10],[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	35	[10]	4	[10]
Revenue net of purchased power and fuel expense, Total	45	[10]	14	[10]
Generation Reportable Segments Total [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	3,601		2,528
Intersegment revenues	47		4
Revenues	3,554	[7]	2,524
Revenue net of purchased power and fuel expense from external customers	1,686	[8]	1,678	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	29		4
Revenue net of purchased power and fuel expense, Total	1,715		1,682
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	3,533		2,743
Revenues	3,533	[7]	2,743
Generation Total Consolidated Group [Member] | All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	(47)	[11]
Revenue net of purchased power and fuel expense from external customers	(322)	[11],[12],[8]	21	[11],[12],[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(29)	[11],[12]	(4)	[11]
Revenue net of purchased power and fuel expense, Total	(351)	[11],[12]	17	[11],[12]
Generation Total Consolidated Group [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	0
Revenue net of purchased power and fuel expense from external customers	1,364	[8]	1,699	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	0
Revenue net of purchased power and fuel expense, Total	1,364		1,699
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	(68)	[11]	215	[11]
Intersegment revenues			(4)	[11]
Revenues	(21)	[11],[7]	219	[11]
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,160	[1]	1,388	[1]
Intersegment revenues	1	[3]	1	[3]
Net income (loss)	(81)		87
Total assets	23,256				22,905
Commonwealth Edison Co [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	60		61
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	895	[1]	875	[1]
Intersegment revenues	0	[3]	1	[3]
Net income (loss)	122		97
Total assets	9,491				9,353
PECO Energy Co [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	34		34
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	880	[1],[13]	52	[1],[13]
Intersegment revenues	4	[13],[3]	1	[13],[3]
Net income (loss)	80	[13]	(65)	[13]
Total assets	7,639	[13]			7,506	[13]
Baltimore Gas and Electric Company [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	$ 22		$ 3

[1] For the three months ended March 31, 2013 and 2012, utility taxes of $21 million and $13 million, respectively, are included in revenues and expenses for Generation. For the three months ended March 31, 2013 and 2012, utility taxes of $60 million and $61 million, respectively, are included in revenues and expenses for ComEd. For the three months ended March 31, 2013 and 2012, utility taxes of $34 million and $34 million, respectively, are included in revenues and expenses for PECO. For the three months ended March 31, 2013 and for the period March 12, 2012 through March 31, 2012, utility taxes of $22 million and $3 million, respectively, are included in revenues and expenses for BGE.

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

[3] 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 3 – Regulatory Matters of the Exelon 2012 Form 10-K for additional information on AECs. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations.

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

[5] 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.

[6] 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, 2013 include revenue from sales to PECO of $ 141 million and sales to BGE of $113 million in the Mid-Atlantic region, and sales to ComEd of $145 million in the Midwest region, net of $ (17) 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, 2012 intersegment revenues for Generation 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.

[7] (a)        Includes all electric sales to third parties and affiliated sales to ComEd, PECO and BGE.

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

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

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

[11]         Other represents activities not allocated to a region. See text above for a description of included activities. Also includes amortization of intangible assets related to commodity contracts recorded at fair value at the merger date of $174 million and $122 million, for the three months ended March 31, 2013 and 2012, respectively.

[12] 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.

[13] 2012 amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through March 31, 2012.