Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013 ReportableSegments		Sep. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 6,502	[1]	$ 6,579	[1]	$ 18,725	[2]	$ 17,235	[2]
Income taxes	439		161		733		445
Net income (loss)	736		297		1,235		787
Total assets	79,661				79,661				78,561
Segment Reporting Additional Information [Abstract]
Number of reportable segments					9
Unrealized Gain (Loss) on Derivatives					229		377
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(668)	[1]	(798)	[1]	(2,003)	[2]	(2,291)	[2]
Total assets	(11,488)				(11,488)				(12,316)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues					1,042	[3]
Exelon Generation Co L L C [Member]
Segment Reporting Additional Information [Abstract]
Number of reportable segments					6
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	373	[4],[5]	459	[4],[5]	1,083	[6],[7]	1,233	[6],[7]
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	4,255	[1],[5]	4,031	[1],[5]	11,858	[2],[7]	10,539	[2],[7]
Net income (loss)	485	[5]	87	[5]	795	[7]	419	[7]
Total assets	40,498	[5]			40,498	[5]			40,681	[5]
Segment Reporting Additional Information [Abstract]
Utility taxes	21		28		60		60
Exelon Generation Co L L C [Member] | Operating Segments [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	144				356		223
Exelon Generation Co L L C [Member] | Operating Segments [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	143		180		409		631
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives	0		(15)		(7)		(30)
Exelon Generation Co L L C [Member] | Operating Segments [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	82		171		321		407
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,391		1,417		3,943		3,789
Revenue net of purchased power and fuel expense, Total	864		908		2,475		2,561
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	10		(11)		11		(43)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	7		(11)		(2)		(44)
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,381	[8]	1,428	[8]	3,932	[3]	3,832	[3]
Revenue net of purchased power and fuel expense from external customers	857	[9]	919	[9]	2,477	[9]	2,605	[9]
Generation Mid Atlantic [Member] | Operating Segments [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues			120
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,013		1,200		3,271		3,619
Revenue net of purchased power and fuel expense, Total	601		730		2,001		2,310
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(5)		7		(3)		19
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(5)		7		(1)		19
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,018	[8]	1,193	[8]	3,274	[3]	3,600	[3]
Revenue net of purchased power and fuel expense from external customers	606	[9]	723	[9]	2,002	[9]	2,291	[9]
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	340		391		933		812
Revenue net of purchased power and fuel expense, Total	62		81		142		180
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(1)		1		(9)		36
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	10		1		(14)		36
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	341	[8]	390	[8]	942	[3]	776	[3]
Revenue net of purchased power and fuel expense from external customers	52	[9]	80	[9]	156	[9]	144	[9]
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	184		185		527		372
Revenue net of purchased power and fuel expense, Total	(9)		13		(17)		60
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(14)		2		(20)		(22)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(38)		2		(31)		(22)
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	198	[8]	183	[8]	547	[3]	394	[3]
Revenue net of purchased power and fuel expense from external customers	29	[9]	11	[9]	14	[9]	82	[9]
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	427		533		1,034		1,074
Revenue net of purchased power and fuel expense, Total	144		158		357		312
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(3)		1		(8)		1
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(78)				(120)		1
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	430	[8]	532	[8]			1,073	[3]
Revenue net of purchased power and fuel expense from external customers	222	[9]	158	[9]	477	[9]	311	[9]
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	271	[10]	329	[10]	737	[10]	651	[10]
Revenue net of purchased power and fuel expense, Total	41	[11]	42	[11]	147	[11]	90	[11]
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(7)	[10]	12	[10]	29	[10]	40	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(75)	[11]	12	[11]	(91)	[11]	41	[11]
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	278	[10],[8]	317	[10],[8]	708	[10],[3]	611	[10],[3]
Revenue net of purchased power and fuel expense from external customers	116	[11],[9]	30	[11],[9]	238	[11],[9]	49	[11],[9]
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,626		4,055		10,445		10,317
Revenue net of purchased power and fuel expense, Total	1,703		1,932		5,105		5,513
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(20)		12				31
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(179)		11		(259)		31
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	3,646	[8]	4,043	[8]	10,445	[3]	10,286	[3]
Revenue net of purchased power and fuel expense from external customers	1,882	[9]	1,921	[9]	5,364	[9]	5,482	[9]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,255		4,031		11,858		10,539
Revenue net of purchased power and fuel expense from external customers	2,076	[9]	1,909	[9]
Revenue net of purchased power and fuel expense, Total	2,076		1,909		5,564		5,521
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues			0				0
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	0		0
Generation Total Consolidated Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	4,255	[8]	4,031	[8]	11,858	[3]	10,539	[3]
Revenue net of purchased power and fuel expense from external customers					5,564	[9]	5,521	[9]
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	629	[12]	(24)	[12]	1,413	[13]	222	[13]
Revenue net of purchased power and fuel expense, Total			(23)	[14]	459	[15]	8	[15]
Generation All Other Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	609	[12],[8]	(12)	[12],[8]	1,413	[13],[3]	253	[13],[3]
Revenue net of purchased power and fuel expense from external customers	194	[14],[9]	(12)	[14],[9]	200	[15],[9]	39	[15],[9]
Segment Reporting Additional Information [Abstract]
Amortization of intangible assets related to commodity contracts	125		404		603		1,089
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel	44		257		386		793
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	20	[12]	(12)	[12]			(31)	[13]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	179	[14]	(11)	[14]	259	[15]	(31)	[15]
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1	[4]	0	[4]	2	[6]	2	[6]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,156	[1]	1,484	[1]	3,395	[2]	4,154	[2]
Net income (loss)	126		90		140		219
Total assets	23,686				23,686				22,905
Segment Reporting Additional Information [Abstract]
Utility taxes	65		67		182		182
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1	[4]	1	[4]	1	[6]	3	[6]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	728	[1]	806	[1]	2,295	[2]	2,396	[2]
Net income (loss)	92		123		292		300
Total assets	9,745				9,745				9,353
Segment Reporting Additional Information [Abstract]
Utility taxes	33		40		97		108
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	2	[4]	4	[4]	10	[16],[6]	7	[16],[6]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	737	[1]	720	[1]	2,271	[16],[2]	1,388	[16],[2]
Net income (loss)	53				160	[16]	(50)	[16]
Total assets	7,657				7,657				7,506
Segment Reporting Additional Information [Abstract]
Utility taxes	20		20		62		42
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	373	[14]
Corporate and Other [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	294	[1],[17]	336	[1],[17]	909	[18],[2]	1,049	[18],[2]
Net income (loss)	(20)	[17]	(3)	[17]	(152)	[18]	(101)	[18]
Total assets	9,563	[17]			9,563	[17]			10,432	[17]
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	294	[17],[4]	337	[17],[4]	909	[18],[6]	1,050	[18],[6]
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	$ 2	[4]	$ 3	[4]	$ 2	[6]	$ 4	[6]

[1] For the three months ended September 30, 2013 and 2012, utility taxes of $21 million and $28 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2013 and 2012, utility taxes of $65 million and $67 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2013 and 2012, utility taxes of $33 million and $40 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2013 and 2012, utility taxes of $20 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2013 and 2012, utility taxes of $60 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2013 and 2012, utility taxes of $182 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2013 and 2012, utility taxes of $97 million and $108 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2013 and period of March 12, 2012 through September 30, 2012, utility taxes of $62 million and $42 million, respectively, are included in revenues and expenses for BGE.

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

[4] Intersegment revenues exclude sales to unconsolidated affiliate entities. The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations.

[5] 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 September 30, 2013 include revenue from sales to PECO of $ 82 million and sales to BGE of $ 144 million in the Mid-Atlantic region, and sales to ComEd of $ 143 million in the Midwest. For the three months ended September 30, 2012 intersegment revenues for Generation include revenue from sales to PECO of $171 million and sales to BGE of $120 million in the Mid-Atlantic region, and sales to ComEd of $180 million in the Midwest region, net of $15 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation.

[6] Intersegment revenues exclude sales to unconsolidated affiliate entities. The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations

[7] 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 nine months ended September 30, 2013 include revenue from sales to PECO of $ 321 million and sales to BGE of $ 356 million in the Mid-Atlantic region, and sales to ComEd of $ 409 million in the Midwest region, net of $ 7 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the nine months ended September 30, 2012 intersegment revenues for Generation include revenue from sales to PECO of $407 million in the Mid-Atlantic region and sales to BGE of $223 million in the Mid-Atlantic region, and sales to ComEd of $631 million in the Midwest region, net of $30 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation.

[8] Includes all electric sales to third parties and affiliated sales to ComEd, PECO and BGE.

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

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

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

[12] 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 of $125 million and $404 million, for the three months ended September 30, 2013 and 2012, respectively, and elimination of intersegment revenues.

[13] 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 $603 million and $1,089 million, for the nine months ended September 30, 2013 and 2012, respectively, and elimination of intersegment revenues.

[14] 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 of $44 million and $257 million for the three months ended September 30, 2013 and 2012, respectively.

[15] 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 $386 million and $793 million, for the nine months ended September 30, 2013 and 2012, respectively.

[16] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through September 30, 2012.

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

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