Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013 ReportableSegments		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	$ 6,141	[1]	$ 5,966	[1]	$ 12,223	[2]	$ 10,656	[2]
Intersegment revenues					0	[3]	1	[3]
Revenues	6,141		5,966		12,223		10,656
Income taxes	239		126		294		284
Net income (loss)	497		289		498		490
Total assets	78,420				78,420				78,561
Segment Reporting Additional Information [Abstract]
Number of reportable segments					9
Unrealized Gain (Loss) on Derivatives					28		323
All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	297	[1],[4]	363	[1],[4]	615	[2],[5]	714	[2],[5]
Intersegment revenues	298	[4]	362	[4]	615	[3],[5]	715	[3],[5]
Net income (loss)	(30)	[4]	(14)	[4]	(132)	[5]	(99)	[5]
Total assets	9,763	[4]			9,763	[4]			10,432	[4]
Business Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	(631)	[1]	(774)	[1]	(1,334)	[2]	(1,494)	[2]
Intersegment revenues	(631)		(774)		(1,334)	[3]	(1,494)	[3]
Total assets	(11,745)				(11,745)				(12,316)
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	4,070	[1],[6]	3,765	[1],[6]	7,603	[2],[7]	6,508	[2],[7]
Intersegment revenues	329	[6]	408	[6]	710	[3],[7]	774	[3],[7]
Net income (loss)	328	[6]	165	[6]	310	[7]	332	[7]
Total assets	39,678	[6]			39,678	[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	18		19		39		32
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	99		84		212		103
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	121		203		266		451
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives	10		(4)		(7)		(15)
Exelon Generation Co L L C [Member] | Reportable Segment [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	97		125		238		235
Generation Mid Atlantic [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,229		1,405		2,552		2,371
Intersegment revenues	9		(28)		1		(33)
Revenues	1,220	[8]	1,433	[8]	2,551	[9]	2,404	[9]
Revenue net of purchased power and fuel expense from external customers	770	[10]	911		1,622	[10]	1,686	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(2)		(28)		(10)		(33)
Revenue net of purchased power and fuel expense, Total	768		883		1,612		1,653
Generation Midwest [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,071		1,201		2,259		2,419
Intersegment revenues	(5)		8		2		12
Revenues	1,076	[8]	1,193	[8]	2,257	[9]	2,407	[9]
Revenue net of purchased power and fuel expense from external customers	687	[10]	756		1,397	[10]	1,569	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(3)		8		4		12
Revenue net of purchased power and fuel expense, Total	684		764		1,401		1,581
Generation New England [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	189		328		592		421
Intersegment revenues	(20)		32		(8)		35
Revenues	209	[8]	296	[8]	600		386	[9]
Revenue net of purchased power and fuel expense from external customers	85	[10]	28		103	[10]	64	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(35)		32		(23)		35
Revenue net of purchased power and fuel expense, Total	50		60		80		99
Generation New York [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	174		144		343		187
Intersegment revenues	(1)		(22)		(7)		(24)
Revenues	175	[8]	166	[8]	350	[9]	211	[9]
Revenue net of purchased power and fuel expense from external customers	0	[10]	61		(16)	[10]	71	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	14		(22)		8		(24)
Revenue net of purchased power and fuel expense, Total	14		39		(8)		47
Generation ERCOT [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	315		413		608		541
Intersegment revenues	(4)		1		(4)		0
Revenues	319	[8]	412	[8]	612	[9]	541	[9]
Revenue net of purchased power and fuel expense from external customers	143	[10]	118		255	[10]	153	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(31)		1		(42)
Revenue net of purchased power and fuel expense, Total	112		119		213		153
Generation Other Regions [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	240	[11]	244	[11]	465	[11]	323	[11]
Intersegment revenues	(6)	[11]	25	[11]	36	[11]	29	[11]
Revenues	246	[11],[8]	219	[11],[8]	429	[11],[9]	294	[11],[9]
Revenue net of purchased power and fuel expense from external customers	111	[10],[12]	9	[12]	122	[10],[12]	19	[10],[12]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(52)	[12]	25	[12]	(17)	[12]	29	[12]
Revenue net of purchased power and fuel expense, Total	59	[12]	34	[12]	105	[12]	48	[12]
Generation Reportable Segments Total [Member] | Reportable Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	3,218		3,735		6,819		6,262
Intersegment revenues	(27)		16		20		19
Revenues	3,245	[8]	3,719	[8]	6,799	[9]	6,243	[9]
Revenue net of purchased power and fuel expense from external customers	1,796	[10]	1,883		3,483	[10]	3,562	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(109)		16		(80)		19
Revenue net of purchased power and fuel expense, Total	1,687		1,899		3,403		3,581
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	4,070		3,765		7,603		6,508
Intersegment revenues					0		0
Revenues	4,070	[8]	3,765	[8]	7,603	[9]	6,508	[9]
Revenue net of purchased power and fuel expense from external customers	2,124	[10]	1,913		3,489	[10]	3,612	[10]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	0				0
Revenue net of purchased power and fuel expense, Total	2,124		1,913		3,489		3,612
Generation All Other Segments [Member] | All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	852	[13]	30	[13]	784	[14]	246	[14]
Intersegment revenues	27	[13]	(16)	[13]	(20)	[14]	(19)	[14]
Revenues	825	[13],[8]	46	[13],[8]	804	[14],[9]	265	[14],[9]
Revenue net of purchased power and fuel expense from external customers	328	[10],[15]	30	[15]	6	[10],[16]	50	[10],[16]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	109	[15]	(16)	[15]	80	[16]	(19)	[16]
Revenue net of purchased power and fuel expense, Total	437	[15]	14	[15]	86	[16]	31	[16]
Segment Reporting Additional Information [Abstract]
Amortization of intangible assets related to commodity contracts	234		534		478		686
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel	167		414		341		537
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	1,080	[1]	1,281	[1]	2,239	[2]	2,670	[2]
Intersegment revenues	0		1		1	[3]	1	[3]
Net income (loss)	96		42		14		129
Total assets	23,349				23,349				22,905
Segment Reporting Additional Information [Abstract]
Utility taxes							115
Commonwealth Edison Co [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	56		54		117
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	672	[1]	715	[1]	1,567	[2]	1,590	[2]
Intersegment revenues	0		1		0	[3]	2	[3]
Net income (loss)	78		80		200		177
Total assets	9,407				9,407				9,353
Segment Reporting Additional Information [Abstract]
Utility taxes							68
PECO Energy Co [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	31		34		64
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment	653	[1]	616	[1]	1,533	[17],[2]	668	[17],[2]
Intersegment revenues	4		2		8	[17],[3]	3	[17],[3]
Net income (loss)	25		16		106	[17]	(49)	[17]
Total assets	7,968				7,968				7,506
Segment Reporting Additional Information [Abstract]
Utility taxes							22
Baltimore Gas and Electric Company [Member] | Reportable Segment [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes	$ 19		$ 19		$ 41

[1] For the three months ended June 30, 2013 and 2012, utility taxes of $18 million and $19 million, respectively, are included in revenues and expenses for Generation. For the three months ended June 30, 2013 and 2012, utility taxes of $56 million and $54 million, respectively, are included in revenues and expenses for ComEd. For the three months ended June 30, 2013 and 2012, utility taxes of $31 million and $34 million, respectively, are included in revenues and expenses for PECO. For the three months ended June 30, 2013 and 2012, utility taxes of $19 million and $19 million, respectively, are included in revenues and expenses for BGE.

[2] For the six months ended June 30, 2013 and 2012, utility taxes of $ 39 million and $ 32 million, respectively, are included in revenues and expenses for Generation. For the six months ended June 30, 2013 and 2012, utility taxes of $117 million and $115 million, respectively, are included in revenues and expenses for ComEd. For the six months ended June 30, 2013 and 2012, utility taxes of $64 million and $68 million, respectively, are included in revenues and expenses for PECO. For the six months ended June 30, 2013 and period of March 12, 2012 through June 30, 2012, utility taxes of $41 million and $22 million, respectively, are included in revenues and expenses for BGE.

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

[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 June 30, 2013 include revenue from sales to PECO of $ 97 million and sales to BGE of $ 99 million in the Mid-Atlantic region, and sales to ComEd of $ 121 million in the Midwest region, net of $ 10 million related to the unrealized mark-to-market gains related to the ComEd swap, which eliminate upon consolidation. For the three months ended June 30, 2012 intersegment revenues for Generation include revenue from sales to PECO of $125 million and sales to BGE of $84 million in the Mid-Atlantic region, and sales to ComEd of $203 million in the Midwest region, net of $4 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation.

[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 six months ended June 30, 2013 include revenue from sales to PECO of $ 238 million and sales to BGE of $ 212 million in the Mid-Atlantic region, and sales to ComEd of $ 266 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 six months ended June 30, 2012 intersegment revenues for Generation include revenue from sales to PECO of $235 million in the Mid-Atlantic region and sales to BGE of $103 million in the Mid-Atlantic region, and sales to ComEd of $451 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.

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

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

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

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

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

[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 of $234 million and $534 million, for the three months ended June 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 at the merger date of $478 million and $686 million, for the six months ended June 30, 2013 and 2012, respectively, and elimination of intersegment revenues.

[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 of $167 million and $414 million for the three months ended June 30, 2013 and 2012, respectively.

[16] 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 $341 million and $537 million, for the six months ended June 30, 2013 and 2012, respectively.

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