Segment Information - Generation Total Revenues (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]
Revenue from Related Parties	1	[2]	1	[2]
Net income (loss)	738		93
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	154		(760)
Revenues	5,840		4,390
Revenue from Related Parties	211		334
Net income (loss)	485		(185)
Amortization of Intangible Assets	(40)		93
Exelon Generation Co L L C [Member] | Sales Revenue, Goods, Net [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	162		(730)
Amortization of Intangible Assets	(38)		42
Corporate and Other [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	318	[1],[3]	290	[1],[3]
Revenue from Related Parties	316	[2],[3]	290	[2],[3]
Net income (loss)	(84)	[3]	4	[3]
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(534)	[1]	(624)	[1]
Revenue from Related Parties	(533)	[2]	(623)	[2]
Net income (loss)	(1)		(1)
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]
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]
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]
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]
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]
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]
Revenues	212		334
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	2		7
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,352		4,008
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	4,354	[4]	4,011	[4]
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(2)		(3)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,488		382
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	2		3	[5]
Generation All Other Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,486		379	[4],[5]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,840	[4]	4,390	[4]
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0		0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	5,840	[1],[6]	4,390	[1],[6]
Revenue from Related Parties	210	[2],[6]	316	[2],[6]
Net income (loss)	485	[6]	(185)	[6]
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	$ 9		$ 108

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246M0JGQzRCODYwOEI3OTJGM0VFMzEwOTNBRjYwNTk1MjUM}

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246NzEwQ0VGNzJGQTI1RkM2RDgzOUMwOTNBRjYwNUU2MTQM}

[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246QzVGNDk1MTM4RDRDN0NDQjA5MkUwOTNBRjYwNUZCMzMM}

[4] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246MzJCOTc5NTI3RTkyMDA2QTkzQzgwOTNBRjYwNURBRkYM}

[5] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246OTk0RkYxNzA5QzkxOUUyRDM3MDcwOTNBRjYwNTNEMDUM}

[6] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246NTk4QTIxQTlGRTU5OTQxMkFDM0QwOTNBRjYwNTMyMDIM}