Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Amortization of Intangible Assets	$ (17)		$ (88)		$ 22		$ (180)
Unrealized Gain (Loss) on Commodity Contracts	25		(83)		179		(843)
Sales Revenue, Goods, Net [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Amortization of Intangible Assets	(14)		(50)		(24)		(92)
Unrealized Gain (Loss) on Commodity Contracts	235		(14)		(397)		744
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	2,383		1,954		4,792		2,988
Generation Total Consolidated Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,383		1,954		4,792	[1]	2,988	[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	889		920		1,671		1,615
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	875	[1]	906	[1]	1,659		1,690
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	14	[1]	14		12		(75)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	743		605		1,443		1,161
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	745	[1]	604	[1]	1,446		1,134
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(2)		1		(3)		27
Generation New England [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	88		64		246		200
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	94	[1]	88	[1]	271		242
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(6)		(24)		(25)		(42)
Generation New York [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	144		148		332		127
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	139	[1]	142	[1]	313		113
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	5		6		19		14
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	70		59		125		142
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	91	[1]	117	[1]	179		272
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(21)		(58)		(54)		(130)
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	62		75		108		180
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	134	[1]	157	[1]	233		307
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(72)		(82)		(125)		(127)
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	1,996		1,871		3,925		3,425
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,078		2,014		4,101	[1]	3,758	[1]
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(82)		(143)		(176)		(333)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	387	[2]	83	[2]	867		(437)
Generation All Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	305	[1],[2]	(60)	[1],[2]	691		(770)
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	$ 82	[2]	$ 143	[2]	$ 176		$ 333

[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 $14 million decrease to RNF and a $50 million decrease to RNF for the amortization of intangible assets related to commodity contracts for the three months ended June 30, 2015 and 2014, respectively, unrealized mark-to-market gains of $235 million and losses of $14 million for the three months ended June 30, 2015 and 2014, respectively, and the elimination of intersegment revenues.