Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Revenues		$ 7,573	$ 8,830
Net income (loss)		123	738
Derivative, Gain on Derivative			(7)
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,520	1,513
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		470	859
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		203	310
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		163	180
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		223	214
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		3,674	4,352
Generation Reportable Segments Total [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenues			43
Revenue from Related Parties			(43)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,065	1,488
Amortization of intangible assets related to commodity contracts		20	40
Derivative, Gain on Derivative		63	154
Generation All Other Segments [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenues			(43)
Revenue from Related Parties			43
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,739	5,840
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[2]	1,532	1,556
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	471	865
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[2]	218	307
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	163	181
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]	222	212
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	3,695	4,397
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	4,739	5,840
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Net income (loss)		257	485
Other Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[4]	1,044	1,443
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		(1)	2
Net income (loss)		(1)	(1)
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		405	317
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		(695)	(533)
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	(12)	(43)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		(1)	(6)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	(15)	3
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		0	(1)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	1	2
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		(21)	(45)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	21	45
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		0	0
Intersegment Eliminations [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		266	210
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)		$ (164)	$ (84)

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