Commitments and Contingencies (Details) (USD $)	9 Months Ended		0 Months Ended												9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended												9 Months Ended		0 Months Ended		9 Months Ended					0 Months Ended				9 Months Ended		0 Months Ended	6 Months Ended	9 Months Ended																9 Months Ended																						12 Months Ended
	Sep. 30, 2012 Years MW PoundsPerMWh Tons	Sep. 30, 2012 Other Purchase Obligations [Member]	Apr. 12, 2012 Cotter Corporation [Member] Defendants	Feb. 28, 2012 Cotter Corporation [Member] Defendants	Sep. 30, 2012 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2012 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2012 Financial Standby Letter of Credit [Member]		Sep. 30, 2012 Sithe Guarantee [Member]	Sep. 30, 2012 TEG And TEP Guarantee [Member]	Sep. 30, 2012 Nuclear Insurance Premiums [Member]		Sep. 30, 2012 Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Oct. 31, 2007 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] OpenClaims	Sep. 30, 2012 Exelon Generation Co L L C [Member] States NumberOfStates NumberOfGridOperators Years Reactors OpenClaims	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Jan. 31, 2005 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Net Capacity Purchases [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Power Purchases [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Transmission Rights Purchases [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Purchased Energy from Equity Investment [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Solar Facility Construction [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Wind Facility Construction [Member] MW	Sep. 30, 2012 Exelon Generation Co L L C [Member] Other Purchase Obligations [Member]	Apr. 12, 2012 Exelon Generation Co L L C [Member] Cotter Corporation [Member] Defendants	Feb. 28, 2012 Exelon Generation Co L L C [Member] Cotter Corporation [Member] Defendants	Sep. 30, 2012 Exelon Generation Co L L C [Member] Cotter Corporation [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2012 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, 2012 Exelon Generation Co L L C [Member] Nuclear Insurance Premiums [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Jul. 11, 2011 Commonwealth Edison Co [Member] Customers	Jun. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Customers MGPSites ElectricGenerationStation	Jul. 12, 2012 Commonwealth Edison Co [Member] Customers	Sep. 30, 2012 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Renewable Energy Including Renewable Energy Credits [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Other Purchase Obligations [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Trust Preferred Securities [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2012 PECO Energy Co [Member] MGPSites	Sep. 30, 2012 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2012 PECO Energy Co [Member] Alternative Energy Credits [Member]	Sep. 30, 2012 PECO Energy Co [Member] Curtailment Services [Member]	Sep. 30, 2012 PECO Energy Co [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2012 PECO Energy Co [Member] Other Purchase Obligations [Member]	Sep. 30, 2012 PECO Energy Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 PECO Energy Co [Member] Total Accrual For Environmental Loss Contingencies [Member]	Sep. 30, 2012 PECO Energy Co [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 PECO Energy Co [Member] Accrual For MGP Investigation And Remediation [Member]	Sep. 30, 2012 PECO Energy Co [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2012 PECO Energy Co [Member] Trust Preferred Securities [Member]	Sep. 30, 2012 PECO Energy Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Claiments MGPSites	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Curtailment Services [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Public Utilities, Inventory, Fuel [Member]	Sep. 30, 2012 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	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Sixty-Eighth Street Dump [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Financial Standby Letter of Credit [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Trust Preferred Securities [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commercial Commitments [Abstract]
Guarantee Obligations Maximum Exposure	$ 14,794,000,000								$ 2,290,000,000	[1]	$ 200,000,000	$ 95,000,000	$ 2,098,000,000	[2]	$ 10,406,000,000	[3]		$ 6,535,000,000	$ 6,535,000,000																			$ 2,082,000,000	[1]			$ 2,098,000,000	[2]	$ 2,355,000,000	[4]			$ 350,000,000											$ 142,000,000	[1]	$ 200,000,000	$ 208,000,000	[5]	$ 203,000,000											$ 22,000,000	[1]	$ 178,000,000	$ 181,000,000	[6]	$ 251,000,000								$ 1,000,000	[1]	$ 250,000,000	$ 250,000,000	[7]
Commercial Commitments Footnote [Abstract]
Guarantees in support of equity investment															211,000,000																													211,000,000
Estimated net exposure for commercial transaction obligations															1,500,000,000																													500,000,000
Nuclear Insurance [Abstract]
Required nuclear liability insurance per site																		375,000,000	375,000,000
Total of U.S. licensed nuclear reactors																			104
Nuclear financial protection pool value																		12,200,000,000	12,200,000,000
Maximum liability per nuclear incident																					2,100,000,000
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					351,000,000	224,000,000	307,000,000	168,000,000																												35,000,000	47,000,000																		265,000,000	127,000,000	260,000,000	121,000,000													50,000,000	50,000,000	47,000,000	47,000,000						1,000,000
Environmental Issues - MGP Site Contingency [Abstract]
Total number of MGP sites																																																42																26																13
Approved clean-up																																																13																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	5,000,000	5,000,000
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
Environmental Issues - Air [Abstract]
States subject to the Cross State Air Pollution Rule																			28
SO2 emissions allowance impairment																			57,000,000
Emissions allowance balance																		39,000,000	39,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term direct financing leases																		678,000,000	678,000,000
Number Of Stations Violating Clean Air Act																																																6
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			14	15																													14	15
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
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																		64,000,000	64,000,000	49,000,000
Asbestos liability reserve related to open claims																		14,000,000	14,000,000
Open asbestos liability claims																		170	170
Asbestos liability reserve related to anticipated claims																		50,000,000	50,000,000
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 porposed by the ICC that ComEd should not be granted a waiver under Continuous Power Interruption																																																	51,767
Unrecorded Unconditional Purchase Obligation [Abstract]
Purchase Obligations, Due within One Year		434,000,000																275,000,000	275,000,000			111,000,000	[8]	8,000,000	[9]	8,000,000	[10]	148,000,000	263,000,000	192,000,000	100,000,000	248,000,000																		0	[11]	33,000,000	[12]	41,000,000											210,000,000	[13]	3,000,000	4,000,000	55,000,000	61,000,000											201,000,000	[14]	11,000,000	44,000,000	17,000,000
Purchase Obligations, Due within Two Years		217,000,000																1,198,000,000	1,198,000,000			375,000,000	[8]	92,000,000	[9]	32,000,000	[10]	699,000,000	1,252,000,000	650,000,000		110,000,000																		367,000,000	[11]	71,000,000	[12]	34,000,000											413,000,000	[13]	11,000,000		114,000,000	21,000,000											707,000,000	[14]	49,000,000	125,000,000	2,000,000
Purchase Obligations, Due within Three Years		135,000,000																891,000,000	891,000,000			352,000,000	[8]	62,000,000	[9]	26,000,000	[10]	451,000,000	1,298,000,000			91,000,000																		323,000,000	[11]	73,000,000	[12]	6,000,000											130,000,000	[13]	9,000,000		68,000,000	17,000,000											263,000,000	[14]	47,000,000	72,000,000
Purchase Obligations, Due within Four Years		94,000,000																386,000,000	386,000,000			350,000,000	[8]	23,000,000	[9]	13,000,000	[10]		1,279,000,000			69,000,000																		136,000,000	[11]	74,000,000	[12]	5,000,000											36,000,000	[13]	2,000,000		53,000,000	1,000,000													41,000,000	52,000,000
Purchase Obligations, Due within Five Years		32,000,000																277,000,000	277,000,000			266,000,000	[8]	9,000,000	[9]	2,000,000	[10]		929,000,000			8,000,000																		137,000,000	[11]	76,000,000	[12]	5,000,000													2,000,000		31,000,000	1,000,000													17,000,000	51,000,000
Purchase Obligations, Due after Five Years		137,000,000																716,000,000	716,000,000			672,000,000	[8]	8,000,000	[9]	36,000,000	[10]		3,647,000,000			29,000,000																		140,000,000	[11]	1,367,000,000	[12]	24,000,000													8,000,000		91,000,000	8,000,000														313,000,000
Purchase Obligations, Total		$ 1,049,000,000																$ 3,743,000,000	$ 3,743,000,000			$ 2,126,000,000	[8]	$ 202,000,000	[9]	$ 117,000,000	[10]	$ 1,298,000,000	$ 8,668,000,000			$ 555,000,000																		$ 1,103,000,000	[11]	$ 1,694,000,000	[12]	$ 115,000,000											$ 789,000,000	[13]	$ 35,000,000	$ 4,000,000	$ 412,000,000	$ 109,000,000											$ 1,171,000,000	[14]	$ 165,000,000	$ 657,000,000	$ 19,000,000
Unrecorded Unconditional Purchase Obligation, Additional Information [Abstract]
Unrecorded Unconditional Purchase Obligation, Related Megawatts																															400
Percentage of ownership interest in CENG (as a percent)																		50.01%	50.01%
Unrecorded Unconditional Purchase Obligation, Related Megawatts, Under Construction																															272

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

[2] Does not include potential maximum combined retrospective premium obligations of CENG amounting to $691 million of which Generation's ownership interest is 50.01%.

[3] 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 $1.5 billion at September 30, 2012, which represents the total amount Exelon could be required to fund based on September 30, 2012 market prices.

[4] 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 $0.5 billion at September 30, 2012, which represents the total amount Generation could be required to fund based on September 30, 2012 market prices.

[5] Primarily reflects full and unconditional guarantees of $200 million Trust Preferred Securities of ComEd Financing III.

[6] Primarily reflects full and unconditional guarantees of $178 million Trust Preferred Securities of PECO Trust III and IV.

[7] Primarily reflects full and unconditional guarantees of $250 million Trust Preferred Securities of BGE Capital Trust II.

[8] 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, 2012, 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. Expected payments include certain capacity charges which are contingent on plant availability.

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

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

[11] ComEd entered into various contracts for the procurement of electricity that expire between 2012 and 2017. ComEd is permitted to recover its electric supply procurement costs from retail customers with no mark-up. See Note 4 - Regulatory Matters for additional information.

[12] ComEd entered into various contracts for the procurement of renewable energy and RECs that expire between 2012 and 2032. ComEd is permitted to recover its renewable energy and REC costs from retail customers with no mark-up. If events were to occur such that ComEd is not allowed to recover the costs under these contracts from retail customers, ComEd may elect to reduce the annual quantity purchased under these contracts. See Note 4 - Regulatory Matters for additional information.

[13] PECO entered into various contracts for the procurement of electric supply to serve its default service customers that expire between 2012 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 Program. See Note 4 - Regulatory Matters for additional information.

[14] BGE entered into various contracts for the procurement of electricity that expire between 2012 and 2014. The cost of power under these contracts is recoverable under MDPSC approved fuel clauses. See Note 4 - Regulatory Matters for additional information.