Fair Value of Financial Assets and Liabilities (Fair Value By Balance Sheet Grouping) (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	$ 289,000,000	$ 737,000,000
Long-term debt (including amounts due within one year)	18,715,000,000	12,627,000,000
Long-term debt to financing trusts	649,000,000	390,000,000
Spent nuclear fuel obligation	1,020,000,000	1,019,000,000
Preferred securities of subsidiary	87,000,000	87,000,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		737,000,000
Long-term debt (including amounts due within one year)		14,488,000,000
Long-term debt to financing trusts		358,000,000
Spent nuclear fuel obligation		886,000,000
Preferred securities of subsidiary		79,000,000
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	4,000,000
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	285,000,000
Long-term debt (including amounts due within one year)	20,762,000,000
Long-term debt to financing trusts	650,000,000
Spent nuclear fuel obligation	780,000,000
Preferred securities of subsidiary	83,000,000
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)	38,000,000
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	11,000,000	2,000,000
Long-term debt (including amounts due within one year)	7,383,000,000	3,677,000,000
Spent nuclear fuel obligation	1,020,000,000	1,019,000,000
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		2,000,000
Long-term debt (including amounts due within one year)		4,231,000,000
Spent nuclear fuel obligation		886,000,000
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]
Short-term liabilities	11,000,000
Long-term debt (including amounts due within one year)	7,839,000,000
Spent nuclear fuel obligation	780,000,000
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)	20,000,000
Commonwealth Edison Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	35,000,000
Long-term debt (including amounts due within one year)	5,217,000,000	5,665,000,000
Long-term debt to financing trusts	206,000,000	206,000,000
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)		6,540,000,000
Long-term debt to financing trusts		184,000,000
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]
Short-term liabilities	35,000,000
Long-term debt (including amounts due within one year)	6,297,000,000
Long-term debt to financing trusts	208,000,000
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)	18,000,000
PECO Energy Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	225,000,000	225,000,000
Long-term debt (including amounts due within one year)	2,322,000,000	1,972,000,000
Long-term debt to financing trusts	184,000,000	184,000,000
Preferred securities of subsidiary	87,000,000	87,000,000
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities		225,000,000
Long-term debt (including amounts due within one year)		2,295,000,000
Long-term debt to financing trusts		174,000,000
Preferred securities of subsidiary		79,000,000
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	225,000,000
Long-term debt (including amounts due within one year)	2,682,000,000
Long-term debt to financing trusts	180,000,000
Preferred securities of subsidiary	83,000,000
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)	2,210,000,000	2,101,000,000
Long-term debt to financing trusts	258,000,000	258,000,000
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)		2,377,000,000
Long-term debt to financing trusts		256,000,000
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)	2,547,000,000
Long-term debt to financing trusts	$ 264,000,000