Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					6 Months Ended
	Jun. 30, 2014		Sep. 30, 2013	Jun. 30, 2013		Jun. 30, 2014 ReportableSegments		Jun. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 6,024		$ 6,141	$ 6,141		$ 13,261	[1]	$ 12,223	[1]
Operating revenues from affiliates	0			0
Income taxes	277			239		224		294
Net income (loss)	557			497				498
Total assets	83,656					83,656				79,924
Segment Reporting Additional Information [Abstract]
Number of reportable segments						9
Unrealized Gain (Loss) on Derivatives						(751)		28
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues						(1,155)	[1]	(1,334)	[1]
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues						441	[2]
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						517	[3],[4]	710	[3],[4]
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	3,789			4,070		8,179	[1],[4]	7,603	[1],[4]
Operating revenues from affiliates	201			329
Net income (loss)	372			328		188	[4]	310	[4]
Total assets	44,422					44,422				41,232
Segment Reporting Additional Information [Abstract]
Utility taxes	21			18		45		39
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	87					207		212
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	65			121		173		266
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives	0			(10)				(7)
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	49			97		137		238
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,277			1,229		2,695		2,552
Revenue net of purchased power and fuel expense, Total	920			768		1,615		1,612
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	5			9		(18)		1
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	14			(2)		(75)		(10)
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,272	[5]		1,220	[5]	2,713	[2]	2,551	[2]
Revenue net of purchased power and fuel expense from external customers	906	[6]		770	[6]	1,690	[6]	1,622	[6]
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues				99
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	981			1,071		2,251		2,259
Revenue net of purchased power and fuel expense, Total	605			684		1,161		1,401
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0			(5)		12		2
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	1			(3)		27		4
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	981	[5]		1,076	[5]	2,239	[2]	2,257	[2]
Revenue net of purchased power and fuel expense from external customers	604	[6]		687	[6]	1,134	[6]	1,397	[6]
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	212			189		761		592
Revenue net of purchased power and fuel expense, Total	64			50		200		80
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1			(20)		5		(8)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(24)			(35)		(42)		(23)
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	211	[5]		209	[5]	756	[2]	600	[2]
Revenue net of purchased power and fuel expense from external customers	88	[6]		85	[6]	242	[6]	103	[6]
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	194			174		381		343
Revenue net of purchased power and fuel expense, Total	148			14		127		(8)
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0			(1)		(3)		(7)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	6			14		14		8
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	194	[5]		175	[5]	384	[2]	350	[2]
Revenue net of purchased power and fuel expense from external customers	142	[6]		0	[6]	113	[6]	(16)	[6]
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	197			315		440		608
Revenue net of purchased power and fuel expense, Total	59			112		142		213
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(1)			(4)		(1)		(4)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(58)					(130)		(42)
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	198	[5]		319	[5]			612	[2]
Revenue net of purchased power and fuel expense from external customers	117	[6]		143	[6]	272	[6]	255	[6]
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	308	[7]		240	[7]	649	[7]	465	[7]
Revenue net of purchased power and fuel expense, Total	75	[7]		59	[7]	180	[7]	105	[7]
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(6)	[7]		(6)	[7]	1	[7]	36	[7]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(82)	[7]		(52)	[7]	(127)	[7]	(17)	[7]
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	314	[5],[7]		246	[5],[7]	648	[2],[7]	429	[2],[7]
Revenue net of purchased power and fuel expense from external customers	157	[6],[7]		111	[6],[7]	307	[6],[7]	122	[6],[7]
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,169			3,218		7,177		6,819
Revenue net of purchased power and fuel expense, Total	1,871			1,687		3,425		3,403
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(1)			(27)		(4)		20
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	(143)			(109)		(333)		(80)
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	3,170	[5]		3,245	[5]	7,181	[2]	6,799	[2]
Revenue net of purchased power and fuel expense from external customers	2,014	[6]		1,796	[6]	3,758	[6]	3,483	[6]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	3,789			4,070		8,179		7,603
Revenue net of purchased power and fuel expense from external customers	1,954	[6]		2,124	[6]
Revenue net of purchased power and fuel expense, Total	1,954			2,124		2,988		3,489
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues				0		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	3,789	[5]		4,070	[5]	8,179	[2]	7,603	[2]
Revenue net of purchased power and fuel expense from external customers						2,988	[6]	3,489	[6]
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	620	[8]		852	[8]	1,002	[9]	784	[9]
Revenue net of purchased power and fuel expense, Total				437	[10]	(437)	[11]	86	[11]
Generation All Other Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	619	[5],[8]		825	[5],[8]	998	[2],[9]	804	[2],[9]
Revenue net of purchased power and fuel expense from external customers	(60)	[10],[6]		328	[10],[6]	(770)	[11],[6]	6	[11],[6]
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	1	[8]		27	[8]	4		(20)	[9]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	143	[10]		109	[10]	333	[11]	80	[11]
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues						1	[3]	1	[3]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,128			1,080		2,262	[1]	2,239	[1]
Operating revenues from affiliates	0			0
Net income (loss)	111			96		209		14
Total assets	24,544					24,544				24,118
Segment Reporting Additional Information [Abstract]
Utility taxes	56			56		119		117
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	0
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues						1	[3]	0	[3]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	656			672		1,649	[1]	1,567	[1]
Operating revenues from affiliates				0
Net income (loss)	84			78		173		200
Total assets	9,761					9,761				9,617
Segment Reporting Additional Information [Abstract]
Utility taxes	30			31		65		64
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues						18	[3]	8	[3]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	653			653		1,707	[1]	1,533	[1]
Operating revenues from affiliates	2			4
Net income (loss)	19			25		106		106
Total assets	7,877					7,877				7,861
Segment Reporting Additional Information [Abstract]
Utility taxes	19			19		43		41
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	83	[10]
Corporate and Other [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	329			297		619	[1],[12]	615	[1],[12]
Operating revenues from affiliates	328			298
Net income (loss)	(29)			(30)		(25)	[12]	(132)	[12]
Total assets	8,769					8,769				8,317
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues						618	[12],[3]	615	[12],[3]
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(531)			(631)		0	[3]	0	[3]
Operating revenues from affiliates	(531)			(631)		(1,155)		(1,334)
Net income (loss)	0			0		0		0
Total assets	$ (11,717)					$ (11,717)				$ (11,221)

[1] For the six months ended June 30, 2014 and 2013, utility taxes of $45 million and $39 million, respectively, are included in revenues and expenses for Generation. For the six months ended June 30, 2014 and 2013, utility taxes of $119 million and $117 million, respectively, are included in revenues and expenses for ComEd. For the six months ended June 30, 2014 and 2013, utility taxes of $65 million and $64 million, respectively, are included in revenues and expenses for PECO. For the six months ended June 30, 2014 and 2013, utility taxes of $43 million and $41 million, respectively, are included in revenues and expenses for BGE.

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

[3] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with the Generation’s 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

[4] 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, 2014 include revenue from sales to PECO of $ 137 million and sales to BGE of $ 207 million in the Mid-Atlantic region, and sales to ComEd of $ 173 million in the Midwest region. For the six months ended June 30, 2013 intersegment revenues for Generation include revenue from sales to PECO of $238 million in the Mid-Atlantic region 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.

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

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

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

[8] 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 date of merger with Constellation and the consolidation of CENG in purchase accounting of $88 million and $234 million, for the three months ended June 30, 2014 and 2013, respectively, and elimination of intersegment revenues.

[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 date of merger with Constellation and the consolidation of CENG in purchase accounting of $180 million and $478 million, for the six months ended June 30, 2014 and 2013, respectively, and elimination of intersegment revenues.

[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 at the date of merger with Constellation and the consolidation of CENG in purchase accounting of $50 million and $167 million for the three months ended June 30, 2014 and 2013, respectively

[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 date of merger with Constellation and the consolidation of CENG in purchase accounting of $92 million and $341 million, for the six months ended June 30, 2014 and 2013, respectively.

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