Fair Value of Financial Assets and Liabilities (Fair Value By Balance Sheet Grouping) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt to financing trusts	$ 648.00	$ 390.00
Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	214.00	737.00
Long-term debt (including amounts due within one year)	18,745.00	12,627.00
Long-term debt to financing trusts	648.00	390.00
Spent nuclear fuel obligation	1,020.00	1,019.00
Preferred securities of subsidiary	87.00	87.00
Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		737.00
Long-term debt (including amounts due within one year)		14,488.00
Long-term debt to financing trusts		358.00
Spent nuclear fuel obligation		886.00
Preferred securities of subsidiary		79.00
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	4.00
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	210.00
Long-term debt (including amounts due within one year)	20,244.00
Spent nuclear fuel obligation	763.00
Preferred securities of subsidiary	82.00
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	276.00
Long-term debt to financing trusts	664.00
Exelon Generation Co L L C [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		2.00
Long-term debt (including amounts due within one year)	7,483.00	3,677.00
Spent nuclear fuel obligation	1,020.00	1,019.00
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		2.00
Long-term debt (including amounts due within one year)		4,231.00
Spent nuclear fuel obligation		886.00
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	7,591.00
Spent nuclear fuel obligation	763.00
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	258.00
Commonwealth Edison Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	5,567.00	5,665.00
Long-term debt to financing trusts	206.00	206.00
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)		6,540.00
Long-term debt to financing trusts		184.00
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	6,530.00
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	18.00
Long-term debt to financing trusts	212.00
PECO Energy Co [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt to financing trusts	184.00	184.00
PECO Energy Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	210.00	225.00
Long-term debt (including amounts due within one year)	1,947.00	1,972.00
Long-term debt to financing trusts	184.00	184.00
Preferred securities of subsidiary	87.00	87.00
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		225.00
Long-term debt (including amounts due within one year)		2,295.00
Long-term debt to financing trusts		174.00
Preferred securities of subsidiary		79.00
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	210.00
Long-term debt (including amounts due within one year)	2,264.00
Preferred securities of subsidiary	82.00
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt to financing trusts	188.00
Baltimore Gas and Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,178.00	2,101.00
Long-term debt to financing trusts	258.00	258.00
Baltimore Gas and Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)		2,377.00
Long-term debt to financing trusts		256.00
Baltimore Gas and Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,468.00
Baltimore Gas and Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt to financing trusts	$ 263.00