Debt and Credit Agreements (Details) (USD $)	3 Months Ended												3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Mar. 31, 2012 Syndicated Revolver [Member]	Mar. 31, 2012 Bilateral Credit Facility [Member]	Mar. 31, 2012 Exelon Corporate [Member] Commercial Paper [Member]	Dec. 31, 2011 Exelon Corporate [Member] Commercial Paper [Member]	Mar. 31, 2012 Exelon Corporate [Member] Long Term Debt Assumed [Member] Notes Two Thousand Thirty Two [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 Exelon Corporate [Member] Long Term Debt Assumed [Member] Notes Two Thousand Fifteen [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 Exelon Corporate [Member] Long Term Debt Assumed [Member] Series A Junior Subordinated Debentures Two Thousand Sixty Three [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 Exelon Corporate [Member] Long Term Debt Assumed [Member] Notes Two Thousand Twenty [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] BasisPoints	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Commercial Paper [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Commercial Paper [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Syndicated Revolver [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Bilateral Credit Facility [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member] Long Term Debt Retirements [Member] Kennett Square Capital Lease Two Thousand Twenty [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] BasisPoints	Dec. 31, 2011 Commonwealth Edison Co [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Commercial Paper [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Commercial Paper [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Syndicated Revolver [Member]	Mar. 31, 2011 Commonwealth Edison Co [Member] Long Term Debt Issuances [Member] First Mortgage Bonds Two Thousand Fourteen [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Long Term Debt Retirements [Member] First Mortgage Bonds Series Ninety Eight Two Thousand Twelve [Member] Fixed Rate Debt [Member]	Mar. 31, 2012 PECO Energy Co [Member]	Dec. 31, 2011 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]	Mar. 31, 2012 PECO Energy Co [Member] Commercial Paper [Member]	Dec. 31, 2011 PECO Energy Co [Member] Commercial Paper [Member]	Mar. 31, 2012 PECO Energy Co [Member] Syndicated Revolver [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Syndicated Revolver [Member]
Credit Agreements [Abstract]
Additional amounts available upon request under current credit facilities																				$ 500,000,000
Basis points adders for prime-based borrowings																				65
Basis points adders for LIBOR-based borrowings																				165
Basis Points For Cash Borrowings																				35
Amount Of Aggregate Letters of Credit Available																				500,000,000
Basis Points For Prime Based Borrowings Current																				27.5
Basis Points For LIBOR Based Borrowings Current																				127.5
Unamortized Debt Issuance Expense																				3,000,000
Previous Aggregate Commitments Of Acquired Entity	2,500,000,000
Amended Aggregate Commitments Of Acquired Entity	1,500,000,000
Accounts Receivable Agreement [Abstract]
Accounts receivable, pledged under accounts receivable agreement			225,000,000	225,000,000																									225,000,000	225,000,000
Short-term notes payable - accounts receivable agreement	225,000,000	225,000,000																									225,000,000	225,000,000
Gross accounts receivable pledged as collateral	348,000,000	329,000,000	348,000,000	329,000,000																							348,000,000	329,000,000	348,000,000	329,000,000
DOE loan guarantee													646,000,000
Basis point spread on DOE loan advance													37.5
DOE interest rate swap	485,000,000												485,000,000
DOE advances received													69,000,000
DOE Interest Rate Swap Loan Advance													52,000,000
Generation letters of credit outstanding to support project													689,000,000
Long-Term Debt [Abstract]
Long-term debt	16,293,000,000	11,799,000,000							700,000,000	550,000,000	450,000,000	550,000,000	6,388,000,000	3,674,000,000					1,000,000	5,215,000,000	5,215,000,000				600,000,000	450,000,000	1,597,000,000	1,597,000,000						1,596,000,000	1,596,000,000
Long-term debt to financing trusts	648,000,000	390,000,000																		206,000,000	206,000,000						184,000,000	184,000,000						258,000,000	258,000,000
Line Of Credit Facility [Abstract]
Aggregate bank commitments under unsecured revolving credit facilities	11,360,000,000				2,000,000,000	1,560,000,000											5,300,000,000	300,000,000						1,000,000,000									600,000,000			600,000,000
Outstanding borrowings/facility draws																																		599,000,000
Short Term Debt [Line Items]
Commercial paper borrowings	$ 0	$ 0					$ 0	$ 161,000,000							$ 0	$ 0						$ 302,000,000	$ 0								$ 0	$ 0