Commitments and Contingencies (Details) (USD $)	0 Months Ended	3 Months Ended	9 Months Ended		0 Months Ended											9 Months Ended					1 Months Ended		9 Months Ended															9 Months Ended						0 Months Ended				9 Months Ended			0 Months Ended	9 Months Ended	12 Months Ended															9 Months Ended																9 Months Ended						9 Months Ended							9 Months Ended
	Feb. 28, 2012 Defendants	Jun. 30, 2013	Sep. 30, 2013 T	Sep. 30, 2013 Other Purchase Obligations [Member]	Apr. 12, 2012 Cotter Corporation [Member] Defendants	Sep. 30, 2013 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2013 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2013 Financial Standby Letter of Credit [Member]		Sep. 30, 2013 Sithe Guarantee [Member]	Sep. 30, 2013 TEG And TEP Guarantee [Member]	Sep. 30, 2013 Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Revenues [Member]		Sep. 30, 2013 Operating And Maintenance Expense [Member]	Jan. 31, 2013 Exelon Generation Co L L C [Member]	Oct. 31, 2007 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Reactors States OpenClaims	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Jan. 31, 2005 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Net Capacity Purchases [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Power Purchases [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Transmission Rights Purchases [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Purchased Energy from Equity Investment [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Solar Facility Construction [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Other Purchase Obligations [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Perryman Construction [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Beebe Construction [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Cotter Corporation [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Rossville ash site [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Financial Standby Letter of Credit [Member]		Jan. 31, 2005 Exelon Generation Co L L C [Member] Sithe Guarantee [Member]	Feb. 09, 2007 Exelon Generation Co L L C [Member] TEG And TEP Guarantee [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Operating And Maintenance Expense [Member]	Jul. 11, 2011 Commonwealth Edison Co [Member] Customers	Sep. 30, 2013 Commonwealth Edison Co [Member] ElectricGenerationStation Customers MGPSites	Dec. 31, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2013 Commonwealth Edison Co [Member] Renewable Energy Including Renewable Energy Credits [Member]		Sep. 30, 2013 Commonwealth Edison Co [Member] Other Purchase Obligations [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2013 Commonwealth Edison Co [Member] Trust Preferred Securities [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2013 PECO Energy Co [Member] MGPSites	Sep. 30, 2013 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2013 PECO Energy Co [Member] Alternative Energy Credits [Member]	Sep. 30, 2013 PECO Energy Co [Member] Curtailment Services [Member]	Sep. 30, 2013 PECO Energy Co [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2013 PECO Energy Co [Member] Other Purchase Obligations [Member]	Sep. 30, 2013 PECO Energy Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 PECO Energy Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2013 PECO Energy Co [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 PECO Energy Co [Member] Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2013 PECO Energy Co [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2013 PECO Energy Co [Member] Trust Preferred Securities [Member]	Sep. 30, 2013 PECO Energy Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Claiments MGPSites	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Curtailment Services [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Other Purchase Obligations [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Sixty-Eighth Street Dump [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Trust Preferred Securities [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Revenues [Member]		Sep. 30, 2013 Midwest Generation, LLC [Member]
Business Acquisition, Costs Recognized Post Merger [Abstract]
BGE rate credit of $100 per residential customer																		$ 113,000,000	[1]																																																																														$ 113,000,000	[1]
Customer investment fund to invest in energy efficiency and low-income energy assistance to BGE customers																				113,500,000
Contribution for renewable energy, energy efficiency or related projects in Baltimore																				2,000,000
Length of years for charitable contributions at $7 million per year			10 years
Business Acquisition Charitable Contributions Per Year			7,000,000																	70,000,000																														35,000,000																																		28,000,000
State funding for offshore wind development projects																				32,000,000
Miscellaneous tax benefits			(2,000,000,000)																																																																																	(2,000,000,000)
Total			328,500,000																				35,000,000																																																													139,000,000
Business Acquisition, Costs Recognized Post Merger Footnotes [Abstract]
Business Acquisition, Equity Contribution		66,000,000
Commercial Commitments [Abstract]
Guarantee Obligations Maximum Exposure			9,518,000,000							1,514,000,000	[2]	200,000,000	95,000,000	3,096,000,000	[3]	4,908,000,000	[4]						5,830,000,000																			1,463,000,000	[2]			3,096,000,000	[3]	1,271,000,000	[5]			235,000,000											26,000,000	[2]	200,000,000	209,000,000	[6]	203,000,000											22,000,000	[2]	178,000,000	181,000,000	[7]	253,000,000								1,000,000	[2]	250,000,000	252,000,000	[8]
Commercial Commitments Footnote [Abstract]
Guarantees in support of equity investment																211,000,000																																211,000,000
Estimated net exposure for commercial transaction obligations																600,000,000																																200,000,000
Nuclear Insurance [Abstract]
Nuclear insurance liability limit per incident																																														13,600,000,000
Required nuclear liability insurance per site																							375,000,000
Total of U.S. licensed nuclear reactors																							104
Nuclear financial protection pool value																							13,200,000,000
Maximum assessment mandated by Price-Anderson Act per nuclear reactor for a nuclear incident																																														127,300,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident																																														19,000,000
Maximum liability per nuclear incident																									3,100,000,000																					2,800,000,000
Guarantees Related To Indemnifications [Abstract]
Acquisition of interest in subsidiary																																												50.00%
Sale of interest in subsidiary																																												100.00%	49.50%
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities						345,000,000	351,000,000	280,000,000	298,000,000																															56,000,000	42,000,000																		237,000,000	261,000,000	232,000,000	254,000,000													51,000,000	47,000,000	48,000,000	44,000,000						1,000,000							1,000,000
Environmental Issues - MGP Site Contingency [Abstract]
Total number of MGP sites																																																				42																26																13
Approved clean-up																																																				16																16
Sites under study/remediation																																																				26																10																2
MGP reserve update																																																					1,000,000															6,000,000
Environmental Issues - Water [Abstract]
Low end of range of cooling tower cost			430,000,000																				430,000,000
Consent decree penalty																						1,000,000
Environmental loss contingencies																						30,000,000	15,000,000																																																																												8,000,000
Increase in accrual due to purchase accounting																							3,000,000
Increase in accrual due to an update of costs																							2,000,000
Environmental Issues - Air [Abstract]
States subject to the Cross State Air Pollution Rule																							28
Emissions allowance balance																							64,000,000
Number Of Stations Violating Clean Air Act																																																				6
Coal Rail Car Lease Proof of Claims																																																				21,000,000
Probable contingency (liability)																							17,000,000																																																																												3,000,000
Payments for operating leases																					10,000,000
Environmental Issues - Solid and Hazardous Waste [Abstract]
DOJ potential settlement																																						90,000,000
Total cost of remediation to be shared by PRPs																																						42,000,000
Loss Contingency Number Of Defendants	15				14
Loss Contingency Number Of Parties Jointly And Severally Liable In Environmental Protection Agency Action																																																																																										19
Loss Contingency Esitmate to close site																																							6,000,000
68th Street and Sauer Dumps [Abstract]
Minimum estimated clean-up costs for all potentially responsible parties																																																																																										50,000,000
Maximum estimated clean-up costs for all potentially responsible parties																																																																																				1,700,000						64,000,000
Climate Change Regulation [Abstract]
Minimum GHG emissions by stationary sources to qualify for regulation			100,000
Minimum additional GHG emissions by stationary sources after a modification			75,000
Effective Number Of Years For Tailoring Rule			6 years
Asbestos Loss Contingency [Abstract]
Asbestos liability reserve																							65,000,000	63,000,000
Asbestos liability reserve related to open claims																							17,000,000																																																																												3,000,000
Open asbestos liability claims																							211
Asbestos liability reserve related to anticipated claims																							48,000,000
Asbestos reserve adjustment
Number of claimants																																																																																				480
US Department Of Energy Settlements [Abstract]
Preacquisition contingency asset DOE settlement gain																							16,000,000
Continuous Power Interruption [Abstract]
Minimum number of customers ComEd can be held liable to for power interruption																																																				30,000
Number of customers affected by a major storm																																																			900,000
Number of customers proposed by the ICC that ComEd should not be granted a waiver under Continuous Power Interruption																																																			34,559
Securities Class Action Suit [Abstract]
Expected settlement amount to resolve class action suit			4,000,000
Unrecorded Unconditional Purchase Obligation [Abstract]
Purchase Obligations, Due within One Year				33,000,000																			296,000,000			86,000,000	[9]	17,000,000	[10]	7,000,000	[11]	186,000,000	339,000,000	180,000,000	133,000,000																			142,000,000	[12]	20,000,000	[13]	7,000,000											211,000,000	[14]	1,000,000	0	54,000,000	19,000,000											227,000,000	[15]	13,000,000	46,000,000	2,000,000
Purchase Obligations, Due within Two Years				38,000,000																			1,291,000,000			396,000,000	[9]	124,000,000	[10]	26,000,000	[11]	745,000,000	1,199,000,000		178,000,000		52,000,000																	323,000,000	[12]	67,000,000	[13]	41,000,000											584,000,000	[14]	2,000,000		128,000,000	25,000,000											669,000,000	[15]	46,000,000	123,000,000	21,000,000
Purchase Obligations, Due within Three Years				32,000,000																			478,000,000			368,000,000	[9]	97,000,000	[10]	13,000,000	[11]	0	1,233,000,000		127,000,000	80,000,000																		136,000,000	[12]	74,000,000	[13]	5,000,000											91,000,000	[14]	2,000,000		100,000,000	1,000,000											226,000,000	[15]	41,000,000	52,000,000	2,000,000
Purchase Obligations, Due within Four Years				31,000,000																			344,000,000			285,000,000	[9]	57,000,000	[10]	2,000,000	[11]		1,021,000,000		40,000,000																			137,000,000	[12]	76,000,000	[13]	5,000,000											0	[14]	2,000,000		78,000,000	1,000,000													34,000,000	51,000,000
Purchase Obligations, Due within Five Years				31,000,000																			241,000,000			223,000,000	[9]	16,000,000	[10]	2,000,000	[11]		1,050,000,000		38,000,000																			140,000,000	[12]	77,000,000	[13]	5,000,000													2,000,000		36,000,000	1,000,000													13,000,000	50,000,000
Purchase Obligations, Due after Five Years				104,000,000																			565,000,000			526,000,000	[9]	5,000,000	[10]	34,000,000	[11]		3,059,000,000		112,000,000																			0	[12]	1,290,000,000	[13]	19,000,000													6,000,000		81,000,000	7,000,000														281,000,000
Purchase Obligations, Total				$ 269,000,000																			$ 3,215,000,000			$ 1,884,000,000	[9]	$ 316,000,000	[10]	$ 84,000,000	[11]	$ 931,000,000	$ 7,901,000,000		$ 628,000,000																			$ 878,000,000	[12]	$ 1,604,000,000	[13]	$ 82,000,000											$ 886,000,000	[14]	$ 15,000,000	$ 0	$ 477,000,000	$ 54,000,000											$ 1,122,000,000	[15]	$ 147,000,000	$ 603,000,000	$ 25,000,000
Unrecorded Unconditional Purchase Obligation, Additional Information [Abstract]
Percentage of ownership interest in CENG (as a percent)																							50.01%

[1] ____________________ (a)        Exelon made a $66 million equity contribution to BGE in the second quarter of 2012 to fund the after-tax amount of the rate credit as directed in the MDPSC order approving the merger transaction.

[2] Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties.

[3] Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.

[4] Primarily reflects parental guarantees issued on behalf of Generation to allow the flexibility needed to conduct business with counterparties without having to post other forms of collateral. Also reflects guarantees issued to ensure performance under specific contracts, preferred securities of financing trusts, property leases, indemnifications, NRC minimum funding assurance requirements and $211 million on behalf of CENG nuclear generating facilities for credit support and miscellaneous guarantees. The estimated net exposure for obligations under commercial transactions covered by these guarantees was $0.6 billion at September 30, 2013, which represents the total amount Exelon could be required to fund based on September 30, 2013 market prices.

[5] Primarily reflects guarantees issued to ensure performance under energy marketing and other specific contracts and $211 million on behalf of CENG nuclear generating facilities for credit support. The estimated net exposure for obligations under commercial transactions covered by these guarantees was $0.2 billion at September 30, 2013, which represents the total amount Generation could be required to fund based on September 30, 2013 market prices.

[6] Primarily reflects full and unconditional guarantees of $200 million Trust Preferred Securities of ComEd Financing III, which is a 100% owned finance subsidiary of ComEd.

[7] Primarily reflects full and unconditional guarantees of $178 million Trust Preferred Securities of PECO Trust III and IV, which are 100% owned finance subsidiaries of PECO.

[8] Primarily reflects full and unconditional guarantees of $250 million Trust Preferred Securities of BGE Capital Trust II, which is a 100% owned finance subsidiary of BGE.

[9] Net capacity purchases include PPAs and other capacity contracts including those that are accounted for as operating leases. Amounts presented in the commitments represent Generation's expected payments under these arrangements at September 30, 2013, net of fixed capacity payments expected to be received by Generation under contracts to resell such acquired capacity to third parties under long-term capacity sale contracts. These capacity payments represent the fixed, or pre-determined, payment for output from contracted generation facilities. Output in this context generally includes products such as energy, capacity, and various ancillary services associated with generating facilities. Expected payments include certain capacity charges which are contingent on plant availability.

[10] Power-related purchases include firm REC purchase agreements. The table excludes renewable energy purchases that are contingent in nature.

[11] Transmission rights purchases include estimated commitments for additional transmission rights that will be required to fulfill firm sales contracts.

[12] (a)        ComEd entered into various contracts for the procurement of electricity that started to expire in 2012, and will continue to expire through 2017. ComEd is permitted to recover its electric supply procurement costs from retail customers with no mark-up. See Note 5 – Regulatory Matters for additional information.

[13] (b)        ComEd entered into 20-year contracts for renewable energy and RECs beginning June 2012. ComEd is permitted to recover its renewable energy and REC costs from retail customers with no mark-up. Pursuant to the ICC’s Order on December 19, 2012, ComEd’s commitments under the existing long-term contracts for energy and associated RECs were reduced in the first quarter of 2013. See Note 5 – Regulatory Matters for additional information.

[14] PECO entered into various contracts for the procurement of electric supply to serve its default service customers that expire between 2013 and 2015. PECO is permitted to recover its electric supply procurement costs from default service customers with no mark-up in accordance with its PAPUC-approved DSP Programs. See Note 5 - Regulatory Matters for additional information.

[15] BGE has entered into various contracts with curtailment services providers related to transactions in PJM's capacity market. See Note 5 - Regulatory Matters for additional information.