Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Feb. 28, 2003	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months		$ 28.00
Future amortization expense in year two		29.00
Future mortizationExpense in year three		29.00
Future amortization expense in year four		29.00
Future amortization expense in year five		29.00
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross		576.00
Finite lived intangible assets accumulated amortization		(132.00)
Finite lived intangible assets net		444.00
Finite Lived Intangible Assets Amortization Expense [Abstract]
Intangible asset amortization expense		20.00		19.00	8.00
Exelon Generation Co L L C [Member]
Finite Lived Intangible Assets Amortization Expense [Abstract]
Intangible asset amortization expense		13.00		12.00	1.00
Renewable Energy Credits And Alternative Energy Credits [Abstract]
Noncurrent alternative or renewable energy credits		45.00		6.00
Exelon Generation Co L L C [Member] | Exelon Wind Acquisition [Member]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months		14.00	[1]
Future amortization expense in year two		14.00	[1]
Future mortizationExpense in year three		14.00	[1]
Future amortization expense in year four		14.00	[1]
Future amortization expense in year five		14.00	[1]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross		224.00	[1]
Finite lived intangible assets accumulated amortization		(26.00)	[1]
Finite lived intangible assets net		198.00	[1]
Exelon Generation Co L L C [Member] | Antelope Valley Acquisition [Member]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months		7.00	[2]
Future amortization expense in year two		8.00	[2]
Future mortizationExpense in year three		8.00	[2]
Future amortization expense in year four		8.00	[2]
Future amortization expense in year five		8.00	[2]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross		190.00	[2]
Finite lived intangible assets accumulated amortization		0	[2]
Finite lived intangible assets net		190.00	[2]
Commonwealth Edison Co [Member]
Finite Lived Intangible Assets Footnotes [Abstract]
2003 City of Chicago payment made to 3rd party	(2.00)
2003 City of Chicago payment received	32.00
2003 City of Chicago payment made to city	(60.00)
Reduction of amortization expense	(2.00)
Finite Lived Intangible Assets Amortization Expense [Abstract]
Intangible asset amortization expense		7.00		7.00	7.00
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months		3.00	[3]
Future amortization expense in year two		3.00	[3]
Future mortizationExpense in year three		3.00	[3]
Future amortization expense in year four		3.00	[3]
Future amortization expense in year five		4.00	[3]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross		100.00	[3]
Finite lived intangible assets accumulated amortization		(72.00)	[3]
Finite lived intangible assets net		28.00	[3]
Commonwealth Edison Co [Member] | Intangible Asset Two Thousand Three Chicago Settlement Agreement [Member]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months		4.00	[4]
Future amortization expense in year two		4.00	[4]
Future mortizationExpense in year three		4.00	[4]
Future amortization expense in year four		4.00	[4]
Future amortization expense in year five		3.00	[4]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross		62.00	[4]
Finite lived intangible assets accumulated amortization		(34.00)	[4]
Finite lived intangible assets net		28.00	[4]
PECO Energy Co [Member]
Renewable Energy Credits And Alternative Energy Credits [Abstract]
Current alternative or renewable energy credits		17.00		14.00
Noncurrent alternative or renewable energy credits		$ 9.00		$ 16.00

[1] Refer to Note 4 – Merger and Acquisitions for additional information regarding Exelon Wind.

[2] Refer to Note 4 – Merger and Acquisitions for additional information regarding Antelope Valley.

[3] In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd's franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020.

[4] In February 2003, ComEd entered into separate agreements with the City of Chicago and with Midwest Generation, LLC (Midwest Generation). Under the terms of the settlement agreement with the City of Chicago, ComEd agreed to pay the City of Chicago a total of $60 million over a ten-year period, beginning in 2003. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement, which ends in 2020. As required by the settlement, ComEd also made a payment of $2 million to a third party on the City of Chicago's behalf. Under the terms of the agreement with Midwest Generation, ComEd received payments of $32 million from Midwest Generation to relieve Midwest Generation's obligation under the 1999 fossil sale agreement with ComEd to build the generation facility in the City of Chicago. The payments received by ComEd, which have been recorded in other long-term liabilities, are being recognized ratably (approximately $2 million annually) as an offset to amortization expense over the remaining term of the franchise agreement.