Debt and Credit Agreements (Details) (USD $)	12 Months Ended																			12 Months Ended			12 Months Ended				12 Months Ended		12 Months Ended				12 Months Ended				12 Months Ended							12 Months Ended															12 Months Ended				12 Months Ended			12 Months Ended	9 Months Ended	12 Months Ended							12 Months Ended				0 Months Ended							12 Months Ended											12 Months Ended																12 Months Ended					12 Months Ended									12 Months Ended
	Dec. 31, 2012 CreditAgreementThreshold BasisPoints		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 ComEd Financing Three Affiliate [Member]		Dec. 31, 2011 ComEd Financing Three Affiliate [Member]		Dec. 31, 2012 PECO Trust Three Affiliate [Member]		Dec. 31, 2011 PECO Trust Three Affiliate [Member]		Dec. 31, 2012 PECO Trust Four Affiliate [Member]		Dec. 31, 2011 PECO Trust Four Affiliate [Member]		Dec. 31, 2012 Baltimore Gas Electric Trust [Member]		Dec. 31, 2012 Rate Stabilization Bonds, April 1, 2017 [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Dec. 31, 2011 Capital Lease Obligations [Member]	Dec. 31, 2012 Notes Payable To Banks [Member]		Dec. 31, 2011 Notes Payable To Banks [Member]		Dec. 31, 2012 Senior Notes [Member]	Dec. 31, 2011 Senior Notes [Member]	Dec. 31, 2012 First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2011 First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2012 First Mortgage Bonds [Member] Floating Rate Debt [Member]	Dec. 31, 2012 Pollution Control Notes [Member]	Dec. 31, 2012 Pollution Control Notes [Member] Fixed Rate Debt [Member]	Dec. 31, 2011 Pollution Control Notes [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 Non Recourse Debt [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 Non Recourse Debt [Member] Floating Rate Debt [Member]	Jun. 28, 2012 Long Term Debt Assumed [Member]	Dec. 31, 2012 Long Term Debt Assumed [Member] Fixed Rate Note, 4.55% Due 2015 [Member]	Dec. 31, 2012 Long Term Debt Assumed [Member] Series A Junior Subordinated Debentures, 8.625% Due 2063 [Member]	Dec. 31, 2012 Long Term Debt Assumed [Member] Notes, 5.15% Due 2020 [Member]	Dec. 31, 2012 Long Term Debt Exchange Offer Exchanged [Member] Senior Notes, 7.6% Due 2032 [Member]	Dec. 31, 2012 Exelon Corporate [Member] BasisPoints		Dec. 31, 2011 Exelon Corporate [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] BasisPoints CreditAgreementThreshold		Dec. 31, 2011 Exelon Generation Co L L C [Member]		Apr. 05, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Capital Lease Obligations [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Capital Lease Obligations [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Notes Payable To Banks [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Notes Payable To Banks [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Senior Notes [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Senior Notes [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Pollution Control Notes [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Pollution Control Notes [Member] Fixed Rate Debt [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Pollution Control Notes [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Constellation Solar Horizons Financing [Member] MW	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Constellation Solar Horizons Financing [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Sacramento PV Energy [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Sacramento PV Energy [Member] MW	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Secured Solar Credit Lending Agreement [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Holyoke [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Denver International Airport [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Upstream Gas Property [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Non Recourse Debt [Member] Floating Rate Debt [Member]	Jun. 18, 2012 Exelon Generation Co L L C [Member] Long Term Debt Issuances [Member] Senior Notes, 4.25% June 15, 2022 [Member]	Jun. 18, 2012 Exelon Generation Co L L C [Member] Long Term Debt Issuances [Member] Senior Notes, 5.6% June 15, 2042 [Member]	Jun. 28, 2012 Exelon Generation Co L L C [Member] Long Term Debt Assumed [Member]	Jun. 18, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Issued And Sold [Member]	Jun. 18, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Issued And Sold [Member] Senior Notes [Member]	Jun. 28, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Purchased [Member]	Jul. 13, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Exchanged [Member]	Jun. 28, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Exchanged [Member]	Jun. 18, 2012 Exelon Generation Co L L C [Member] Long Term Debt Exchange Offer Exchanged [Member] Senior Notes, 7.6% Due 2032 [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] CreditAgreementThreshold		Dec. 31, 2011 Commonwealth Edison Co [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] ComEd Financing Three Affiliate [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member] ComEd Financing Three Affiliate [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Notes Payable To Banks [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Notes Payable To Banks [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member] First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2012 PECO Energy Co [Member] CreditAgreementThreshold BasisPoints		Dec. 31, 2011 PECO Energy Co [Member]		Dec. 31, 2012 PECO Energy Co [Member] PECO Trust Three Affiliate [Member]		Dec. 31, 2011 PECO Energy Co [Member] PECO Trust Three Affiliate [Member]		Dec. 31, 2012 PECO Energy Co [Member] PECO Trust Four Affiliate [Member]		Dec. 31, 2011 PECO Energy Co [Member] PECO Trust Four Affiliate [Member]		Dec. 31, 2012 PECO Energy Co [Member] First Mortgage Bonds [Member]	Dec. 31, 2012 PECO Energy Co [Member] First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2011 PECO Energy Co [Member] First Mortgage Bonds [Member] Fixed Rate Debt [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] CreditAgreementThreshold BasisPoints		Dec. 31, 2011 Baltimore Gas and Electric Company [Member]		Dec. 31, 2010 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Baltimore Gas Electric Trust [Member]		Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Baltimore Gas Electric Trust [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Rate Stabilization Bonds, April 1, 2017 [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Rate Stabilization Bonds, April 1, 2017 [Member]
Credit Agreements [Abstract]
Additional amounts available upon request under current credit facilities	$ 250,000,000																																															$ 1,000,000,000																																						$ 500,000,000															$ 250,000,000																	$ 100,000,000
Amount that would constitute an event of default																																																100,000,000
Basis points adders for prime-based borrowings																																												0.00275				0.00075																																																																						0.00075
Basis points adders for LIBOR-based borrowings																																												0.01275				0.01075																																																					0.01																	0.01075
Letters Of Credit	200,000,000																																															3,500,000,000																																						500,000,000															300,000,000																	600,000,000
Bilateral letters of credit																																																75,000,000
Basis Points For Prime Based Borrowings Current	0.0065
Basis Points For LIBOR Based Borrowings Current	0.0165
Previous Aggregate Commitments Of Acquired Entity	2,500,000,000
Amended Aggregate Commitments Of Acquired Entity	1,500,000,000
Aggregate bank commitments under amendment	500,000,000																																															5,300,000,000																																						1,000,000,000															600,000,000																	600,000,000
Accounts Receivable Agreement [Abstract]
Accounts receivable, pledged under accounts receivable agreement	225,000,000																																																																																																				225,000,000
Short-term notes payable - accounts receivable agreement	210,000,000		225,000,000																																																																																																		210,000,000		225,000,000
Accounts receivable, principal payment																																																																																																					15,000,000
Gross accounts receivable pledged as collateral	289,000,000		346,000,000																																																																																																		289,000,000		329,000,000
AVSR Project Development Debt Agreement [Abstract]
DOE loan guarantee																																																646,000,000
Basis point spread on DOE loan advance																																																0.00375
DOE interest rate swap																																																485,000,000
DOE advances received																																																219,000,000				69,000,000
Generation letters of credit outstanding to support project																																																568,000,000
Debt Covenant [Line Items]
Credit agreement interest coverage minimum threshold	2.50																																															3.00																																						2.00															2.00																	2.00
Interest coverage ratio	9.62																																															14.20																																						6.14															7.85																	5.16
Long-Term Debt [Abstract]
Secured Long Term Debt																													7,397,000,000	[1],[2]	7,522,000,000	[1],[2]																																																																	5,447,000,000	[3],[4]	5,547,000,000	[3],[4]
Unsecured Long Term Debt	1,850,000,000																										8,021,000,000	4,902,000,000																															6,721,000,000	[5]	3,602,000,000	[5]																																																								1,850,000,000		1,710,000,000
Long-term debt to affiliate																																																2,007,000,000											1,808,000,000
Long Term Notes Payable																							177,000,000	[6]	174,000,000	[6]																													30,000,000	[6]	34,000,000	[6]																																					140,000,000	140,000,000
Long Term Pollution Control Bond																																			20,000,000	46,000,000																												20,000,000	46,000,000
Non-recourse debt																																																																			38,000,000	38,000,000	39,000,000	41,000,000	113,000,000	11,000,000	7,000,000	72,000,000
Non-Recourse Debt - MW																																																																			16			30
Non-Recourse Debt - Term																																																																				18 years			3 years
Non-Recourse Debt - Commitment																																																																							150,000,000			150,000,000
Non-Recourse Debt - Commitment Increase Available																																																																							200,000,000			500,000,000
Non-Recourse Debt - Interest Rate Swap																																																																				29,000,000	29,000,000
Non-Recourse Debt - Hedge Percentage																																																																				75.00%	75.00%
Total long-term debt	18,297,000,000		12,644,000,000																																													7,271,000,000		3,682,000,000																																				5,587,000,000		5,687,000,000													1,647,000,000		1,597,000,000															2,182,000,000		2,105,000,000
Unamortized debt discount and premium, net	(17,000,000)		(32,000,000)																																													(13,000,000)		5,000,000																																				20,000,000		22,000,000													3,000,000		3,000,000															4,000,000		4,000,000
Unamortized settled fair value hedge, net	(448,000,000)																																																																																					0		0
Fair value hedge carrying value adjustment, net	17,000,000		15,000,000
Long-term debt due within one year	(1,047,000,000)		(828,000,000)																																													(28,000,000)		(3,000,000)																																				(252,000,000)		(450,000,000)													(300,000,000)		(375,000,000)															(467,000,000)		(173,000,000)
Long-term debt	17,190,000,000		11,799,000,000																	332,000,000																	238,000,000	262,000,000		550,000,000	450,000,000	550,000,000	700,000,000					5,245,000,000		3,674,000,000																									238,000,000	262,000,000						441,000,000	1,000,000			5,315,000,000		5,215,000,000													1,647,000,000		1,597,000,000											1,950,000,000	[7],[8]	1,975,000,000	[7],[8]	1,446,000,000		1,596,000,000							332,000,000	395,000,000
Total long-term debt with adjustments	17,698,000,000																																															7,455,000,000		3,674,000,000																																																																				1,711,000,000		1,928,000,000
Long-term debt to PECO Energy Transition Trust due within one year																																																																																																					0		0
Total long-term debt to financing trusts	648,000,000	[9]	390,000,000	[9]																																																																																																	184,000,000	[10]	184,000,000	[10]																			258,000,000	[11]	258,000,000	[11]
Long-term debt to financing trusts	508,000,000		390,000,000			206,000,000	[9]	206,000,000	[9]	81,000,000	[9]	81,000,000	[9]	103,000,000	[9]	103,000,000	[9]	258,000,000	[9]																																																																			206,000,000		206,000,000			206,000,000	[12]	206,000,000	[12]							184,000,000		184,000,000		81,000,000	[10]	81,000,000	[10]	103,000,000	[10]	103,000,000	[10]						258,000,000		258,000,000			258,000,000	[11]	258,000,000	[11]
Interest rate on long-term debt						6.35%				7.38%				5.75%				6.20%					7.83%																	4.55%	8.63%	5.15%																																			4.25%	5.60%							7.60%						6.35%				6.95%										7.38%				5.75%														6.20%
Minimum interest rate on long-term debt																				5.72%			6.95%				2.00%		1.63%				2.80%	4.10%			2.33%	1.96%																					2.00%				4.10%			2.33%										1.96%																					1.63%																	2.38%				2.80%									5.47%
Maximum interest rate on long-term debt																				5.82%			7.83%				8.63%		7.63%				6.35%	5.00%			5.50%	2.77%																					8.63%				5.00%												5.50%	2.77%																					7.63%																5.95%					6.35%									5.82%
Long Term Debt	18,945,000,000																																															7,271,000,000																																	775,000,000			535,000,000		5,793,000,000															2,134,000,000																	2,440,000,000
Long term debt old notes	258,000,000																																						608,000,000
Cash payment related to exchange offer																																																																																				60,000,000
Increase in fair value adjustment	403,000,000																																																																														13,000,000
Fair Value Adjustment Outstanding	199,000,000																																															199,000,000	[5]
Footnotes To Long-Term Debt [Abstract]
Capital Leases Future Minimum Payments Due Current																					3,000,000																																3,000,000
Capital Leases Future Minimum Payments Due In Two Years																					3,000,000																																3,000,000
Capital Leases Future Minimum Payments Due In Three Years																					3,000,000																																3,000,000
Capital Leases Future Minimum Payments Due In Four Years																					4,000,000																																4,000,000
Capital Leases Future Minimum Payments Due In Five Years																					4,000,000																																4,000,000
Capital Leases Future Minimum Payments Due Thereafter																					13,000,000																																13,000,000
Capital Lease Obligations Noncurrent																					30,000,000	34,000,000																															30,000,000	34,000,000
Notional amount of interest rate cash flow hedge derivatives																																																																																470,000,000
Loss on interest rate swap																																																																																7,000,000
Line Of Credit Facility [Abstract]
Aggregate bank commitments under unsecured revolving credit facilities	8,300,000,000	[13]																																										500,000,000	[13]			5,600,000,000	[13]																																					1,000,000,000	[13]														600,000,000	[13]																600,000,000	[13]
Outstanding borrowings/facility draws	1,821,000,000																																											2,000,000				1,818,000,000																																																					1,000,000
Outstanding letters of credit	200,000,000																																															3,500,000,000																																						500,000,000															300,000,000																	600,000,000
Actual available capacity	6,479,000,000																																											498,000,000				3,782,000,000																																						1,000,000,000															599,000,000																	600,000,000
Available capacity to support additional commercial paper borrowings	6,479,000,000																																											498,000,000				3,782,000,000																																						1,000,000,000															599,000,000																	600,000,000
Footnotes To Line Of Credit Facility [Abstract]
Credit facility agreements with minority and community banks																																																50,000,000																																						34,000,000															34,000,000																	5,000,000
Letters of credit																																																23,000,000																																						21,000,000															21,000,000																	1,000,000
Short Term Debt [Line Items]
Maximum program size	8,300,000,000	[14]	8,100,000,000	[14]																																								500,000,000	[14]	500,000,000	[14]	5,600,000,000	[14]	5,600,000,000	[14]																																			1,000,000,000	[14]	1,000,000,000	[14]												600,000,000	[14]	600,000,000	[14]														600,000,000	[14]	400,000,000	[14]
Commercial paper borrowings			161,000,000																																											161,000,000
Average Interest Rate On Commercial Paper Borrowings																																												0.47%		0.42%		0.45%		0.48%																																						0.71%																														0.43%		0.38%
Short Term Debt Activity [Line Items]
Average borrowings	199,000,000		218,000,000		125,000,000																																											4,000,000		51,000,000																																				110,000,000		36,000,000		125,000,000																												6,000,000		26,000,000		1,000,000
Maximum borrowings outstanding	$ 505,000,000		$ 600,000,000		$ 346,000,000																																											$ 165,000,000		$ 304,000,000																																				$ 366,000,000		$ 407,000,000		$ 346,000,000																												$ 76,000,000		$ 190,000,000		$ 46,000,000
Average interest rates, computed on a daily basis	0.48%		0.50%		0.72%																																											0.45%		0.48%																																				0.50%		0.71%		0.72%																												0.43%		0.38%		0.39%
Average interest rates, at December 31			0.44%

[1] Substantially all of ComEd's assets other than expressly excepted property and substantially all of PECO's assets are subject to the liens of their respective mortgage indentures.

[2] Includes First Mortgage Bonds issued under the ComEd and PECO mortgage indentures securing pollution control bonds and notes.

[3] Substantially all of ComEd's assets other than expressly excepted property are subject to the lien of its mortgage indenture.

[4] Includes First Mortgage Bonds issued under the ComEd mortgage indenture securing pollution control bonds and notes.

[5] Includes $2,007 million of long-term debt to affiliate, comprised of $1,808 million senior unsecured notes and $199 million fair value adjustment.

[6] Includes capital lease obligations of $30 million and $34 million at December 31, 2012 and 2011, respectively. Lease payments of $3 million, $3 million, $3 million, $4 million, $4 million and $13 million will be made in 2013, 2014, 2015, 2016, 2017 and thereafter, respectively.

[7] Substantially all of PECO's assets are subject to the lien of its mortgage indenture.

[8] Includes First Mortgage Bonds issued under the PECO mortgage indenture securing pollution control bonds and notes.

[9] Amounts owed to these financing trusts are recorded as debt to financing trusts within Exelon's Consolidated Balance Sheets.

[10] Amount owed to this financing trust is recorded as debt to financing trust within PECO's Consolidated Balance Sheets.

[11]  (a)        Amount owed to this financing trust is recorded as debt to financing trust within BGE's Consolidated Balance Sheets.

[12] Amount owed to this financing trust is recorded as debt to financing trust within ComEd's Consolidated Balance Sheets.

[13] Excludes additional credit facility agreements for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd's, PECO's and BGE’s service territories. These facilities expire on October 19, 2013 and are solely for issuing letters of credit. As of December 31, 2012, letters of credit issued under these agreements totaled $23 million, $21 million, $21 million and $1 million for Generation, ComEd, PECO and BGE, respectively.

[14] (a) Equals aggregate bank commitments under revolving and bilateral credit agreements. See discussion below and Credit Agreements table below for items affecting effective program size.