Commitments and Contingencies (Details) (USD $)	0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended											3 Months Ended						1 Months Ended		3 Months Ended														3 Months Ended					0 Months Ended				3 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended															3 Months Ended																3 Months Ended						12 Months Ended								3 Months Ended
	Feb. 28, 2012 Defendants	Mar. 31, 2013 PoundsPerMWh T	Jun. 30, 2012	Sep. 30, 2012	Mar. 31, 2013 Other Purchase Obligations [Member]	Apr. 12, 2012 Cotter Corporation [Member] Defendants	Mar. 31, 2013 Climate Change Regulation [Member] MW	Mar. 31, 2013 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Total Accrual For Environmental Loss Contingencies [Member]	Mar. 31, 2013 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Accrual For MGP Investigation And Remediation [Member]	Mar. 31, 2013 Financial Standby Letter of Credit [Member]		Mar. 31, 2013 Sithe Guarantee [Member]	Mar. 31, 2013 TEG And TEP Guarantee [Member]	Mar. 31, 2013 Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Revenues [Member]		Mar. 31, 2013 Operating And Maintenance Expense [Member]	Mar. 31, 2013 Taxes Other Than Income Taxes [Member]	Jan. 31, 2013 Exelon Generation Co L L C [Member]	Oct. 31, 2007 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Reactors NumberOfGridOperators States NumberOfStates OpenClaims	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Jan. 31, 2005 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Net Capacity Purchases [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Power Purchases [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Transmission Rights Purchases [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Purchased Energy from Equity Investment [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Public Utilities, Inventory, Fuel [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Solar Facility Construction [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Wind Facility Construction [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Other Purchase Obligations [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Cotter Corporation [Member]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Operating And Maintenance Expense [Member]	Jul. 11, 2011 Commonwealth Edison Co [Member] Customers	Mar. 31, 2013 Commonwealth Edison Co [Member] MGPSites Customers ElectricGenerationStation	Dec. 31, 2012 Commonwealth Edison Co [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Renewable Energy Including Renewable Energy Credits [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Other Purchase Obligations [Member]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 2013 Commonwealth Edison Co [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Trust Preferred Securities [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2013 PECO Energy Co [Member] MGPSites	Mar. 31, 2013 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]		Mar. 31, 2013 PECO Energy Co [Member] Alternative Energy Credits [Member]	Mar. 31, 2013 PECO Energy Co [Member] Curtailment Services [Member]	Mar. 31, 2013 PECO Energy Co [Member] Public Utilities, Inventory, Fuel [Member]	Mar. 31, 2013 PECO Energy Co [Member] Other Purchase Obligations [Member]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 2013 PECO Energy Co [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2013 PECO Energy Co [Member] Trust Preferred Securities [Member]	Mar. 31, 2013 PECO Energy Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Claiments MGPSites	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Curtailment Services [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Public Utilities, Inventory, Fuel [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Other Purchase Obligations [Member]	Dec. 31, 1999 Baltimore Gas and Electric Company [Member] Sixty-Eighth Street Dump [Member] PrincipleResponsibleParties	Mar. 31, 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]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Trust Preferred Securities [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Revenues [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Taxes Other Than Income Taxes [Member]	Mar. 31, 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)																																																																														(2,000,000)
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		11,617,000,000										1,573,000,000	[2]	200,000,000	95,000,000	2,494,000,000	[3]	7,550,000,000	[4]							5,864,000,000																	1,522,000,000	[2]			2,494,000,000	[3]	1,848,000,000	[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																		1,100,000,000																															400,000,000
Nuclear Insurance [Abstract]
Required nuclear liability insurance per site																										375,000,000
Total of U.S. licensed nuclear reactors																										104
Nuclear financial protection pool value																										12,200,000,000
Maximum liability per nuclear incident																												2,200,000,000
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								337,000,000	338,000,000	296,000,000	298,000,000																														30,000,000	30,000,000																		259,000,000	260,000,000	252,000,000	254,000,000													47,000,000	47,000,000	44,000,000	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																																																					15																16
Sites under study/remediation																																																					27																10																2
MGP reserve update																																																						146,000,000															7,000,000
Number of sites related to portion of MGP reserve update																																																					6
Portion of MGP reserve update																																																					111,000,000
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																									23,000,000	3,000,000
Environmental loss contingencies payments																										18,000,000
Total Conemaugh Station water discharge settlement to be paid by all responsible parties		500,000
Portion of Conemaugh Station water discharge settlement to be paid by Exelon		200,000
Expected economic useful life reduction																										10 years
Environmental Issues - Air [Abstract]
States subject to the Cross State Air Pollution Rule																										28
SO2 emissions allowance impairment																										57,000,000
Emissions allowance balance																										51,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term direct financing leases																										700,000,000
Number Of Stations Violating Clean Air Act																																																					6
Probable contingency (liability)																										16,000,000																																																																												3,000,000
Midwest Generation's estimated environmental investigation and remediation costs				9,000,000
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
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
Minimum wattage subject to new source performance standards							25
Effective Number Of Years For Tailoring Rule		6 years
New source performance standard emissions limit		1,000
New source performance standard emissions limit first ten years		1,800
New source performance standard emissions limit after ten years		600
Asbestos Loss Contingency [Abstract]
Asbestos liability reserve																										62,000,000	63,000,000
Asbestos liability reserve related to open claims																										16,000,000																																																																												3,000,000
Open asbestos liability claims																										189
Asbestos liability reserve related to anticipated claims																										46,000,000
Increase (decrease) in the value of the asbestos liability reserve																										19,000,000
Asbestos reserve adjustment																										19,000,000
Number of claimants																																																																																					480
US Department Of Energy Settlements [Abstract]
Preacquisition contingency asset DOE settlement gain																										16,000,000
FERC Settlement [Abstract]
FERC civil penalty																										135,000,000
FERC disgorgement																										110,000,000
FERC disgorgement portion paid to each of six grid operators																										1,000,000
Number of States in PJM																										13
Number of grid operators in New York ISO																										6
FERC settlement recorded in operation and maintenance expense																										195,000,000
FERC settlement recorded as preacquisition contingency																										50,000,000
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																																																				34,599
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					204,000,000																					940,000,000			274,000,000	[9]	60,000,000	[10]	22,000,000	[11]	584,000,000	940,000,000	304,000,000	100,000,000	135,000,000																367,000,000	[12]	49,000,000	[13]	2,000,000											704,000,000	[14]	10,000,000	0	141,000,000	18,000,000											651,000,000	[15]	37,000,000	104,000,000	0
Purchase Obligations, Due within Two Years					196,000,000																					1,046,000,000			356,000,000	[9]	76,000,000	[10]	26,000,000	[11]	588,000,000	1,239,000,000	650,000,000		141,000,000																323,000,000	[12]	66,000,000	[13]	12,000,000											309,000,000	[14]	5,000,000		103,000,000	19,000,000											466,000,000	[15]	46,000,000	72,000,000	0
Purchase Obligations, Due within Three Years					127,000,000																					400,000,000			351,000,000	[9]	36,000,000	[10]	13,000,000	[11]	0	1,256,000,000			107,000,000																136,000,000	[12]	74,000,000	[13]	0											60,000,000	[14]	2,000,000		75,000,000	1,000,000											74,000,000	[15]	41,000,000	50,000,000
Purchase Obligations, Due within Four Years					61,000,000																					287,000,000			266,000,000	[9]	19,000,000	[10]	2,000,000	[11]		1,021,000,000			41,000,000																137,000,000	[12]	76,000,000	[13]	0											0	[14]	2,000,000		49,000,000	1,000,000													16,000,000	48,000,000
Purchase Obligations, Due within Five Years					58,000,000																					209,000,000			203,000,000	[9]	4,000,000	[10]	2,000,000	[11]		1,068,000,000			38,000,000																140,000,000	[12]	82,000,000	[13]	0													2,000,000		15,000,000	1,000,000													0	48,000,000
Purchase Obligations, Due after Five Years					171,000,000																					509,000,000			472,000,000	[9]	3,000,000	[10]	34,000,000	[11]		3,098,000,000			108,000,000																0	[12]	1,285,000,000	[13]	0													6,000,000		78,000,000	7,000,000														266,000,000
Purchase Obligations, Total					$ 817,000,000																					$ 3,391,000,000			$ 1,922,000,000	[9]	$ 198,000,000	[10]	$ 99,000,000	[11]	$ 1,172,000,000	$ 8,622,000,000			$ 570,000,000																$ 1,103,000,000	[12]	$ 1,632,000,000	[13]	$ 14,000,000											$ 1,073,000,000	[14]	$ 27,000,000	$ 0	$ 461,000,000	$ 47,000,000											$ 1,191,000,000	[15]	$ 140,000,000	$ 588,000,000	$ 0
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 $1.1 billion at March 31, 2013, which represents the total amount Exelon could be required to fund based on March 31, 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 $0.4 billion at March 31, 2013, which represents the total amount Generation could be required to fund based on March 31, 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 is a 100% owned finance subsidiary 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 March 31, 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 associate 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 entered into various contracts for the procurement of electricity that expire between 2013 and 2015. The cost of power under these contracts is recoverable under MDPSC approved fuel clauses. See Note 5 - Regulatory Matters for additional information.