Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 ReportableSegments		Mar. 31, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 7,237	[1]	$ 6,082	[1]
Income taxes	(54)		56
Net income (loss)	93		1
Total assets	79,468		79,924		79,924
Segment Reporting Additional Information [Abstract]
Number of reportable segments	9
Unrealized Gain (Loss) on Derivatives	(730)		(388)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	1		0
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues			3,533
Segment Reporting Additional Information [Abstract]
Number of reportable segments	6
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	4,390	[1],[2]
Operating revenues from affiliates	316		381
Net income (loss)	(185)	[2]	(17)	[2]
Total assets	41,080		41,232
Segment Reporting Additional Information [Abstract]
Utility taxes	24		21
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	120
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	108		145
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives	0		(17)
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	88		141
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,418		1,323
Revenue net of purchased power and fuel expense, Total	695		844
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(23)		(8)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(89)		(8)
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,441	[3],[4]	1,331	[3],[4]
Revenue net of purchased power and fuel expense from external customers	784	[5]	852	[5]
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues			113
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,270		1,188
Revenue net of purchased power and fuel expense, Total	556		717
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	12		7
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	26		7
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,258	[3],[4]	1,181	[3],[4]
Revenue net of purchased power and fuel expense from external customers	530	[5]	710	[5]
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	549		403
Revenue net of purchased power and fuel expense, Total	136		30
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	4		12
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(18)		12
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	545	[3],[4]	391	[3],[4]
Revenue net of purchased power and fuel expense from external customers	154	[5]	18	[5]
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	187		169
Revenue net of purchased power and fuel expense, Total	(21)		(22)
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(3)		(6)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	8		(6)
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	190	[3],[4]	175	[3],[4]
Revenue net of purchased power and fuel expense from external customers	(29)	[5]	(16)	[5]
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	243		293
Revenue net of purchased power and fuel expense, Total	83		101
Generation ERCOT [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	(72)
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	243	[4]	293	[3],[4]
Revenue net of purchased power and fuel expense from external customers	155	[5]	112	[5]
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	341	[6],[7]	225	[6],[7]
Revenue net of purchased power and fuel expense, Total	105	[6],[8]	45	[6],[8]
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	7	[6],[7]	42	[6],[7]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(45)	[6],[8]	35	[6],[8]
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	334	[3],[4],[6],[7]	183	[3],[4],[6],[7]
Revenue net of purchased power and fuel expense from external customers	150	[5],[6],[8]	10	[5],[6],[8]
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,008		3,601
Revenue net of purchased power and fuel expense, Total	1,554		1,715
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(3)		47
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(190)		29
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	4,011	[3],[4]	3,554	[3],[4]
Revenue net of purchased power and fuel expense from external customers	1,744	[5]	1,686	[5]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,390		3,533
Revenue net of purchased power and fuel expense from external customers	1,033	[5]	1,364	[5]
Revenue net of purchased power and fuel expense, Total	1,033		1,364
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues			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	4,390	[3],[4]	3,533	[3],[4]
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	382	[10],[9]	(68)	[10],[9]
Revenue net of purchased power and fuel expense, Total			(351)	[11],[12]
Generation All Other Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	379	[10],[3],[4],[9]	(21)	[10],[3],[4],[9]
Revenue net of purchased power and fuel expense from external customers	(711)	[11],[12],[5]	(322)	[11],[12],[5]
Segment Reporting Additional Information [Abstract]
Amortization of intangible assets related to commodity contracts	125		404
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel	44		257
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	3	[10]	(47)	[10],[9]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	190	[11],[12]	(29)	[11],[12]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,134	[1]	1,160	[1]
Operating revenues from affiliates	1		1
Net income (loss)	98		(81)
Total assets	24,294		24,118
Segment Reporting Additional Information [Abstract]
Utility taxes	63		60
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	993	[1]	895	[1]
Operating revenues from affiliates	1		0
Net income (loss)	89		122
Total assets	9,766		9,617
Segment Reporting Additional Information [Abstract]
Utility taxes	35		34
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,054	[1],[13]	880	[1],[13]
Operating revenues from affiliates	16		4
Net income (loss)	88	[13]	80	[13]
Total assets	7,958		7,861
Segment Reporting Additional Information [Abstract]
Utility taxes	20		22
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	(521)	[11]
Corporate and Other [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	290	[1],[14]	318	[1],[14]
Operating revenues from affiliates	290		318
Net income (loss)	4	[14]	(103)	[14]
Total assets	8,146		8,317
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(624)	[15]	(704)	[15]
Operating revenues from affiliates	(623)		(704)
Net income (loss)	(1)		0
Total assets	$ (11,776)		$ (11,221)

[1] For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<gcytdutiltax> million and $##D<gpytdutiltax> million, respectively, are included in revenues and expenses for Generation. For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<ccytdutiltax> million and $##D<cpytdutiltax> million, respectively, are included in revenues and expenses for ComEd. For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<pcytdutiltax> million and $##D<ppytdutiltax> million, respectively, are included in revenues and expenses for PECO. For the ##D<curmonth> months ended ##D<cyperiod> and period of March 12, 2012 through ##D<pyperiod>, utility taxes of $##D<bcytdutiltax> million and $##D<bpytdutiltax> million, respectively, are included in revenues and expenses for BGE.

[2] 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 ##D<curmonth> months ended ##D<cyperiod> include revenue from sales to PECO of $##D<gcyytdrevPECO> million and sales to BGE of $##D<gcyytdrevBGE> million in the Mid-Atlantic region, and sales to ComEd of $##D<gcyytdrevComEd> million in the Midwest region, net of $##D<gcyytdrevComEdSwap> million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the ##D<curmonth> months ended ##D<pyperiod> intersegment revenues for Generation include revenue from sales to PECO of $##D<gpyytdrevPECO> million in the Mid-Atlantic region and sales to BGE of $##D<gpyytdrevBGE> million in the Mid-Atlantic region, and sales to ComEd of $##D<gpyytdrevComEd> million in the Midwest region, net of $##D<gpyytdrevComEdSwap> million related to the unrealized ma...

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

[4] Includes all electric sales to 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 include the South, West and Canada, which are not considered individually significant.

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

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

[9] 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 $##D<gpurchacctg> million and $##D<gpypurchacctgytd> million, for the ##D<curmonth> months ended ##D<cyperiod> and 2012, respectively.

[10] 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 $93 million and $174 million, for the three months ended March 31, 2014 and 2013, respectively, and elimination of intersegment revenues.

[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 of $42 million and $174 million for the three months ended March 31, 2014 and 2013, respectively

[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 at the merger date of $386 million and $793 million, for the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, respectively.

[13] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through ##D<pyperiod>.

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

[15] 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