Commitments and Contingencies (Details) (USD $)	1 Months Ended	12 Months Ended					12 Months Ended													9 Months Ended	12 Months Ended																									0 Months Ended				12 Months Ended			12 Months Ended															12 Months Ended																		12 Months Ended
	Oct. 31, 2007	Dec. 31, 2012 NumberOfGridOperators MW PoundsPerMWh States Tons OpenClaims		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Other Purchase Obligations [Member]	Dec. 31, 2012 Sauer Dump [Member] Defendants	Dec. 31, 2012 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Financial Standby Letter of Credit [Member]	Dec. 31, 2012 Surety Bond [Member]	Dec. 31, 2012 Property Lease Guarantee [Member]	Dec. 31, 2012 Performance Guarantee [Member]	Dec. 31, 2012 Energy Contract Guarantee [Member]	Dec. 31, 2012 Nuclear Insurance Premiums [Member]	Dec. 31, 2012 Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]	Dec. 31, 2012 Middle market lending commitment [Member]	Sep. 30, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Reactors		Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Net Capacity Purchases [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Power Purchases [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Transmission Rights Purchases [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Purchased Energy from Equity Investment [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Total Unregulated Energy Commitments [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Public Utilities, Inventory, Fuel [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Solar Facility Construction [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Other Purchase Obligations [Member]	Dec. 31, 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]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Financial Standby Letter of Credit [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Performance Guarantee [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Energy Contract Guarantee [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]	Dec. 31, 2012 Exelon Generation Co L L C [Member] TEG And TEP Guarantee [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Nuclear Insurance Premiums [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Middle market lending commitment [Member]	Dec. 31, 2012 Constellation Energy Nuclear Group LLC [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] MGPSites Customers		Dec. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Renewable Energy Including Renewable Energy Credits [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Other Purchase Obligations [Member]	Dec. 31, 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]	Dec. 31, 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]	Dec. 31, 2012 Commonwealth Edison Co [Member] Financial Standby Letter of Credit [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Surety Bond [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Performance Guarantee [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Trust Preferred Securities [Member]	Dec. 31, 2012 PECO Energy Co [Member] TimesLiquidatingValue MGPSites		Dec. 31, 2012 PECO Energy Co [Member] MultipleLiquidatingPreferred MGPSites		Dec. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 PECO Energy Co [Member] Alternative Energy Credits [Member]	Dec. 31, 2012 PECO Energy Co [Member] Public Utilities, Inventory, Fuel [Member]	Dec. 31, 2012 PECO Energy Co [Member] Other Purchase Obligations [Member]	Dec. 31, 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]	Dec. 31, 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]	Dec. 31, 2012 PECO Energy Co [Member] Financial Standby Letter of Credit [Member]	Dec. 31, 2012 PECO Energy Co [Member] Surety Bond [Member]	Dec. 31, 2012 PECO Energy Co [Member] Performance Guarantee [Member]	Dec. 31, 2012 PECO Energy Co [Member] Trust Preferred Securities [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	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] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Curtailment Services [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Public Utilities, Inventory, Fuel [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Other Purchase Obligations [Member]	Dec. 31, 2012 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]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Financial Standby Letter of Credit [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Surety Bond [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Performance Guarantee [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Trust Preferred Securities [Member]	Dec. 31, 2012 Midwest Generation, LLC [Member]	Sep. 30, 2012 Midwest Generation, LLC [Member]
Commercial Commitments [Abstract]
Guarantee Obligations Maximum Exposure		$ 15,350,000,000			$ 200,000,000							$ 1,889,000,000	$ 286,000,000	$ 48,000,000	$ 1,897,000,000	$ 8,556,000,000	$ 2,494,000,000		$ 180,000,000		$ 7,462,000,000																					$ 1,841,000,000	[1]	$ 1,153,000,000	$ 1,794,000,000			$ 95,000,000	$ 2,494,000,000		$ 180,000,000	$ 689,000,000	$ 230,000,000											$ 22,000,000	$ 8,000,000	$ 200,000,000	$ 200,000,000	$ 203,000,000		$ 203,000,000												$ 22,000,000	$ 3,000,000	$ 178,000,000	$ 178,000,000	$ 254,000,000												$ 2,000,000	$ 2,000,000	$ 250,000,000	$ 250,000,000
Guarantee obligations maximum exposure next twelve months		11,194,000,000										1,325,000,000	225,000,000	0	908,000,000	8,556,000,000	0		180,000,000		4,159,000,000																					1,278,000,000	[1]	907,000,000	1,794,000,000				0		180,000,000		30,000,000											22,000,000	8,000,000			25,000,000		25,000,000												22,000,000	3,000,000			4,000,000												2,000,000	2,000,000
Guarantee obligations maximum exposure year two		203,000,000										0	0	0	203,000,000	0	0				203,000,000																					0	[1]	203,000,000	0				0
Guarantee obligations maximum exposure year three		565,000,000										564,000,000	1,000,000	0	0	0	0				563,000,000																					563,000,000	[1]	0	0				0
Guarantee obligations maximum exposure year four		6,000,000										0	6,000,000	0	0	0	0				0																					0	[1]	0	0				0
Guarantee obligations maximum exposure year five		4,000,000										0	4,000,000	0	0	0	0				0																					0	[1]	0	0				0
Guarantee obligations maximum exposure year six and beyond		3,378,000,000										0	50,000,000	48,000,000	786,000,000	0	2,494,000,000				2,537,000,000																					0	[1]	43,000,000	0				2,494,000,000				200,000,000													200,000,000		178,000,000		178,000,000														178,000,000		250,000,000														250,000,000
Commercial Commitments Footnote [Abstract]
Guarantees in support of letters of credit																					0
Guarantees in support of equity investment																																																		211,000,000
Estimated net exposure for commercial transaction obligations																		1,500,000																																600,000
Estimated total assumed for commercial transaction obligations																8,300,000																													1,500,000
Nuclear Insurance [Abstract]
Nuclear insurance liability limit per incident																					12,600,000,000
Required nuclear liability insurance per site																					375,000,000
Total of U.S. licensed nuclear reactors																					104
Nuclear financial protection pool value																					12,200,000,000
Cost surcharge to Price-Anderson Act nuclear incident assessment																					5.00%
Maximum assessment mandated by Price-Anderson Act per nuclear reactor for a nuclear incident																					117,500,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident																					17,500,000
Maximum liability per nuclear incident																					2,200,000,000
Total retrospective premium obligation under insurance from a nuclear industry mutual insurance company																					278,000,000
Total nuclear property insurance coverage																					2,100,000,000
Nuclear property insurance coverage limit per individual insured																					1,250,000,000
Additional nuclear property insurance purchased under single limit blanket property																					850,000,000
Nuclear insurance property damage maximum retrospective premium obligation																					220,000,000
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses																					3,200,000,000
Nuclear outage replacement power cost insurance maximum annual retrospective premium obligation																					58,000,000
Spent Nuclear Fuel Obligation [Abstract]
Cost of spent nuclear fuel disposal per kWh of net nuclear generation																					0.001
Estimate increase in nuclear ARO due to delay in DOE acceptance of spent nuclear fuel for date one																					700,000,000
Reimbursement for spent nuclear fuel costs																					639,000,000
Net reimbursement for spent nuclear fuel cost after co-owner deduction																					543,000,000
Requested SNF reimbursement costs from the DOE																					61,000,000
Requested SNF reimbursement cost owed to co-owners																					13,000,000
Department of Energy SNF one-time fee applicable to nuclear generation																					277,000,000
DOE SNF one-time fee with interest																					1,020,000,000
13-week Treasury Rate used to calculate DOE SNF one-time fee																					0.127%
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								338,000,000	224,000,000	298,000,000	168,000,000																											30,000,000	47,000,000	0	0																			260,000,000	127,000,000	254,000,000	121,000,000															47,000,000	50,000,000	44,000,000	47,000,000													1,000,000	0	0	0
Environmental Issues - MGP Site Contingency [Abstract]
Total number of MGP sites																																																					42															26		26																13,000,000
Approved clean-up																																																					13															16		16
Sites under study/remediation																																																					27															10		10																3,000,000
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
Consent decree penalty	1,000,000
Environmental loss contingencies	23,000,000	3,000,000
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
Environmental Issues - Air [Abstract]
SO2 emissions allowance impairment																				57,000,000
Emissions allowance balance																					45,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term direct financing leases		685,000,000		656,000,000																	693,000,000
Probable contingency (liability)		14,000,000																																																																																																				13,000,000
Midwest Generation's estimated environmental investigation and remediation costs																																																																																																							9,000,000
Environmental Issues - Solid and Hazardous Waste [Abstract]
Total cost of remediation to be shared by PRPs																																																					42,000,000
68th Street and Sauer Dumps [Abstract]
Number of defendants in addition to BGE and Constellation Energy							3
Minimum estimated clean-up costs for all potentially responsible parties																																																																																													50,000,000
Maximum estimated clean-up costs for all potentially responsible parties																																																																																													64,000,000
Climate Change Regulation [Abstract]
Minimum GHG emissions by stationary sources to qualify for regulation		75,000
Minimum additional GHG emissions by stationary sources after a modification		100,000
Minimum wattage subject to new source performance standards		25
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																					69,000,000		49,000,000
Asbestos liability reserve related to open claims		14,000,000																																																																																																				13,000,000
Open asbestos liability claims		170
Asbestos liability reserve related to anticipated claims		49,000,000
Asbestos reserve adjustment																					19,000,000
US Department Of Energy Settlements [Abstract]
Preacquisition contingency asset DOE settlement gain																					16,000,000
Funds received from DOE settlement																					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
Dividend Payments Restrictions [Abstract]
Total of common stock and retained earnings																																																																				3,000,000,000		3,000,000,000
Multiple of liquidating value of preferred stock																																																																				34		34
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																																																					34,599
Unrecorded Unconditional Purchase Obligation [Abstract]
Purchase Obligations, Due within One Year						186,000,000																					374,000,000	[2]	95,000,000	[3]	28,000,000	[4]	777,000,000	1,274,000,000	1,276,000,000	636,000,000	127,000,000																				367,000,000	71,000,000	2,000,000															561,000,000	12,000,000	145,000,000	17,000,000												859,000,000	49,000,000	133,000,000	0
Purchase Obligations, Due within Two Years						167,000,000																					353,000,000	[2]	69,000,000	[3]	26,000,000	[4]	516,000,000	964,000,000	1,207,000,000		120,000,000																				323,000,000	73,000,000	6,000,000															200,000,000	9,000,000	87,000,000	18,000,000												467,000,000	47,000,000	73,000,000	0
Purchase Obligations, Due within Three Years						114,000,000																					350,000,000	[2]	25,000,000	[3]	13,000,000	[4]	0	388,000,000	1,272,000,000		94,000,000																				136,000,000	74,000,000	0															38,000,000	2,000,000	71,000,000	1,000,000												75,000,000	41,000,000	54,000,000	0
Purchase Obligations, Due within Four Years						51,000,000																					266,000,000	[2]	11,000,000	[3]	2,000,000	[4]	0	279,000,000	976,000,000		32,000,000																				137,000,000	76,000,000	0															0	2,000,000	49,000,000	1,000,000												0	16,000,000	52,000,000	0
Purchase Obligations, Due within Five Years						49,000,000																					203,000,000	[2]	3,000,000	[3]	2,000,000	[4]	0	208,000,000	1,064,000,000		29,000,000																				140,000,000	82,000,000	0															0	2,000,000	15,000,000	1,000,000												0	0	52,000,000	0
Purchase Obligations, Due after Five Years						149,000,000																					469,000,000	[2]	5,000,000	[3]	34,000,000	[4]	0	508,000,000	3,062,000,000		85,000,000																				0	1,285,000,000	0															0	6,000,000	77,000,000	7,000,000												0	0	290,000,000	0
Purchase Obligations, Total						716,000,000																					2,015,000,000	[2]	208,000,000	[3]	105,000,000	[4]	1,293,000,000	3,621,000,000	8,857,000,000		487,000,000																				1,103,000,000	1,661,000,000	8,000,000															799,000,000	33,000,000	444,000,000	45,000,000												1,401,000,000	153,000,000	654,000,000	0
Unrecorded Unconditional Purchase Obligation, Additional Information [Abstract]
Percentage of ownership interest in CENG (as a percent)		1.00%
Operating Leases Future Minimum Payments Due Table [Abstract]
Minimum future operating lease payments due in one year		88,000,000																			38,000,000																																13,000,000	[5]														14,000,000	[5]	14,000,000	[5]															12,000,000
Minimum future operating lease payments due in two years		83,000,000																			38,000,000																																11,000,000	[5]														13,000,000	[5]	13,000,000	[5]															10,000,000
Minimum future operating lease payments due in three years		73,000,000																			38,000,000																																11,000,000	[5]														3,000,000	[5]	3,000,000	[5]															9,000,000
Minimum future operating lease payments due in four years		69,000,000																			36,000,000																																11,000,000	[5]														3,000,000	[5]	3,000,000	[5]															7,000,000
Minimum future operating lease payments due in five years		63,000,000																			36,000,000																																6,000,000	[5]														3,000,000	[5]	3,000,000	[5]															6,000,000
Minimum future operating lease payments due beyond five years		488,000,000																			367,000,000																																57,000,000	[5]														0	[5]	0	[5]															29,000,000
Total minimum future operating lease payments		864,000,000	[6]																		553,000,000	[6]																															109,000,000	[5]														36,000,000	[5]	36,000,000	[5]															73,000,000
Future Operating Lease Payments Indefinite Periods Footnote [Abstract]
Future operating lease payments with indefinite periods due in one year																																																					1,000,000																	3,000,000																1,000,000
Future operating lease payments with indefinite periods due in two years																																																					1,000,000
Future operating lease payments with indefinite periods due in three years																																																					1,000,000
Future operating lease payments with indefinite periods due in four years																																																					1,000,000
Future operating lease payments with indefinite periods due in five years																																																					1,000,000
Operating Leases Rent Expense [Abstract]
Lease And Rental Expense		930,000,000		711,000,000	722,000,000																872,000,000	[7]	659,000,000	[7]	665,000,000	[7]																											18,000,000		18,000,000	19,000,000														27,000,000		28,000,000	31,000,000													12,000,000	15,000,000	13,000,000
Operating Leases Rent Expense Footnote [Abstract]
Long Term Contract For Purchase Of Electric Power Capacity																					$ 801,000,000		$ 630,000,000		$ 641,000,000

[1] Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[2] 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 December 31, 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.

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

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

[5] Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO and BGE have excluded these payments from the remaining years, as such amounts would not be meaningful. ComEd's annual obligation for these arrangements, included in each of the years 2013 - 2017, was $1 million. PECO's annual obligation for these agreements, included in each of the years 2013 - 2017, was $3 million. BGE’s annual obligation for these agreements, included in each of the years 2013 - 2017, was $1 million. (c)        Includes all future lease payments on a 99 year real estate lease that expires in 2105.

[6] Excludes Generation's PPAs and other capacity contracts that are accounted for as contingent operating lease payments.

[7] Includes Generation's PPAs and other capacity contracts that are accounted for as operating leases and are reflected as net capacity purchases in the energy commitments table above. These agreements are considered contingent operating lease payments and are not included in the minimum future operating lease payments table above. Payments made under Generation's PPAs and other capacity contracts totaled $801 million, $630 million and $641 million during 2012, 2011 and 2010, respectively.