Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 8,830	[1]	$ 7,237	[1]
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	5,840		4,390
Amortization of Intangible Assets	(40)		93
Unrealized Gain (Loss) on Commodity Contracts	154		(760)
Sales Revenue, Goods, Net [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Amortization of Intangible Assets	(38)		42
Unrealized Gain (Loss) on Commodity Contracts	162		(730)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	5,840	[1],[2]	4,390	[1],[2]
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,513		1,418
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	784	[3]	784	[3]
Intersegment RNF	(2)		(89)
Revenues	1,517		1,441
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(4)		(23)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,276		1,270
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	701	[3]	530	[3]
Intersegment RNF	(1)		26
Revenues	1,275		1,258
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1		12
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	859		549
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	177	[3]	154	[3]
Intersegment RNF	(19)		(18)
Revenues	858		545
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1		4
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	310		187
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	174	[3]	(29)	[3]
Intersegment RNF	14		8
Revenues	310		190
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0		(3)
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	180		243
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	88	[3]	155	[3]
Intersegment RNF	(33)		(72)
Revenues	182		243
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(2)		0
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	214		341
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	99	[3]	150	[3]
Intersegment RNF	(53)		(45)
Revenues	212		334
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	2		7
Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	(94)		(190)
Segment Reporting Information Revenue Net of Purchase Power And Fuel	1,929		1,554
Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,023	[3]	1,744	[3]
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	0		0
Segment Reporting Information Revenue Net of Purchase Power And Fuel	2,407		1,033
Revenues	1,488		382
Generation All Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	384	[3],[4]	(711)	[3],[4]
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	2		3	[5]
Operating Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,407	[3]	1,033	[3]
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	782		695
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	700		556
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	158		136
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	188		(21)
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	55		83
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	46		105
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	94	[4]	190	[4]
Segment Reporting Information Revenue Net of Purchase Power And Fuel	$ 478	[4]	$ (521)	[4]

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