Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Amortization of Intangible Assets	$ 3		$ 22		$ 19		$ 203
Unrealized Gain (Loss) on Commodity Contracts	(7)		271		171		(572)
Sales Revenue, Goods, Net [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Amortization of Intangible Assets	4		15		20		78
Unrealized Gain (Loss) on Commodity Contracts	(139)		267		(258)		477
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	2,249		2,532		7,041		5,520
Generation Total Consolidated Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,249		2,532		7,041	[1]	5,520	[1]
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	0		0		0		0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	991		935		2,663		2,550
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	974	[1]	921	[1]	2,633		2,610
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	17	[1]	14		30		(60)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	752		716		2,195		1,877
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	752	[1]	722	[1]	2,198		1,856
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	0		(6)		(3)		21
Generation New England [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	133		90		379		290
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	145	[1]	120	[1]	416		362
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(12)		(30)		(37)		(72)
Generation New York [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	167		186		498		313
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	159	[1]	176	[1]	471		289
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	8		10		27		24
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	111		109		235		250
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	166	[1]	186	[1]	344		457
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(55)		(77)		(109)		(207)
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	83		68		193		249
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	167	[1]	157	[1]	403		465
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(84)		(89)		(210)		(216)
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	2,237		2,104		6,163		5,529
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,363		2,282		6,465	[1]	6,039	[1]
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(126)		(178)		(302)		(510)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	12	[2]	428	[2]	878		(9)
Generation All Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	(114)	[1],[2]	250	[1],[2]	576		(519)
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	$ 126	[2]	$ 178	[2]	$ 302		$ 510

[1] (a)Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE.

[2] (c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $4 million decrease to RNF and a $15 million increase to RNF for the amortization of intangible assets related to commodity contracts for the three months ended September 30, 2015 and 2014, respectively, unrealized mark-to-market losses of $139 million and gains of $267 million for the three months ended September 30, 2015 and 2014, respectively, and the elimination of intersegment revenues.