Commitments and Contingencies (Details) (USD $)	3 Months Ended					3 Months Ended								1 Months Ended	3 Months Ended	9 Months Ended															3 Months Ended				3 Months Ended					0 Months Ended						3 Months Ended
	Mar. 31, 2012 States MW PoundsPerMWh Reactors	Dec. 31, 2011	Sep. 30, 2011 Tons	Mar. 31, 2012 Financial Standby Letter of Credit [Member]		Mar. 31, 2012 Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2012 Nuclear Insurance Premiums [Member]	Mar. 31, 2012 Parental Guarantee [Member]	Mar. 31, 2012 Total Accrual For Environmental Loss Contingencies [Member]	Dec. 31, 2011 Total Accrual For Environmental Loss Contingencies [Member]	Mar. 31, 2012 Accrual For MGP Investigation And Remediation [Member]	Dec. 31, 2011 Accrual For MGP Investigation And Remediation [Member]	Oct. 31, 2007 Exelon Generation Co L L C [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Reactors MW OpenClaims	Sep. 30, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] One Year From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than One And Within Two Years From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than Four And Within Five Years From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Long Term Contract For Future Purchase Of Electric Power Capacity [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member] Long Term Contract For Purchase Of Electric Power Estimated Annual Cost [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member] Future Transmission Rights Purchase Commitments [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member] Purchased Energy From CENG [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] One Year From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] More Than One And Within Two Years From Balance Sheet Date [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member] Nuclear Insurance Premiums [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] Sithe 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]	Mar. 31, 2012 Exelon Generation Co L L C [Member] TEG And TEP Guarantee [Member]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Customers MGPSites		Mar. 31, 2012 Commonwealth Edison Co [Member] One Year From Balance Sheet Date [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] More Than One And Within Two Years From Balance Sheet Date [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] More Than Four And Within Five Years From Balance Sheet Date [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Nuclear Insurance Premiums [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Trust Preferred Securities [Member]	Mar. 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]	Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] MGPSites		Dec. 31, 2011 PECO Energy Co [Member]	Mar. 31, 2012 PECO Energy Co [Member] One Year From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than One And Within Two Years From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than Four And Within Five Years From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member]	Mar. 31, 2012 PECO Energy Co [Member] One Year From Balance Sheet Date [Member]		Mar. 31, 2012 PECO Energy Co [Member] More Than One And Within Two Years From Balance Sheet Date [Member]		Mar. 31, 2012 PECO Energy Co [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]		Mar. 31, 2012 PECO Energy Co [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]		Mar. 31, 2012 PECO Energy Co [Member] More Than Four And Within Five Years From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member]	Mar. 31, 2012 PECO Energy Co [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2012 PECO Energy Co [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2012 PECO Energy Co [Member] Nuclear Insurance Premiums [Member]	Mar. 31, 2012 PECO Energy Co [Member] Trust Preferred Securities [Member]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] OpenClaims MGPSites		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] One Year From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than One And Within Two Years From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Four And Within Five Years From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] One Year From Balance Sheet Date [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than One And Within Two Years From Balance Sheet Date [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Two And Within Three Years From Balance Sheet Date [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] More Than Three And Within Four Years From Balance Sheet Date [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Financial Standby Letter of Credit [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Nuclear Insurance Premiums [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Trust Preferred Securities [Member]	Mar. 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]	Mar. 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]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities										$ 223,000,000	$ 224,000,000	$ 163,000,000	$ 168,000,000																													$ 51,000,000	$ 47,000,000	$ 0	$ 0																					$ 123,000,000	$ 127,000,000	$ 116,000,000	$ 121,000,000																										$ 49,000,000	$ 50,000,000	$ 46,000,000	$ 47,000,000																						$ 0	$ 0	$ 0	$ 0
Commercial And Construction Commitments [Abstract]
Guarantor Obligations, Current Carrying Value																																																																																																			75,000,000
Guarantee Obligations Maximum Exposure	15,417,000,000			2,623,000,000	[1]	2,100,000,000		2,098,000,000	1,600,000,000						4,927,000,000																		1,381,000,000	[1]	300,000,000		2,098,000,000	200,000,000			95,000,000					232,000,000														23,000,000	[1]	209,000,000	[2]	0	200,000,000					202,000,000																			21,000,000	[1]	181,000,000	[3]	0	178,000,000					254,000,000															1,000,000	[1]	253,000,000	[4]	0	250,000,000
Guarantor Obligations, Related Party Disclosure						211																													205
Guarantee Obligations, Face Amount						10,696,000,000	[5]																												1,448,000,000	[6]
Commercial Commitments Footnote [Abstract]
Guarantees in support of letters of credit	1,000,000														1,000,000
Guarantees Related To Indemnifications [Abstract]
Acquisition of interest in subsidiary																																							50.00%
Sale of interest in subsidiary																																							100.00%	49.50%
Proceeds From Sale Of Equity Method Investments																																								95,000,000
Nuclear Insurance [Abstract]
Required nuclear liability insurance per site	375,000,000														375,000,000
Total of U.S. licensed nuclear reactors	104														104
Nuclear financial protection pool value	12,200,000,000														12,200,000,000
Maximum liability per nuclear incident	2,100,000,000														2,100,000,000
Environmental Issues - MGP Site Contingency [Abstract]
Total number of MGP sites																																														42																								27																													12
Approved clean-up																																														13																								16																													2
Sites under study/remediation																																														27																								9
Environmental Issues - Water [Abstract]
Annual employee retention expense															2,000,000
Low end of range of cooling tower cost	430,000,000														430,000,000
Groundwater Contamination [Abstract]
Consent decree penalty														1,000,000
Environmental loss contingencies														23,000,000	18,000,000
Environmental loss contingencies payments															5,000,000
Conemaugh Station Water Discharge [Abstract]
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
Emission Credits or Allowances [Abstract]
SO2 emissions allowance impairment															36,000,000	57,000,000
Minimum fossil plant MW subject to NSPS	25
Maximum emissions NSPS thirty year average	1,000
Maximum emissions NSPS first ten years	1,800
Maximum emissions NSPS after first ten years	600
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term direct financing leases															663,000,000
Environmental Issues - Solid and Hazardous Waste [Abstract]
Cotter Corporation DOJ potential settlement															100,000,000
Total cost of remediation to be shared by PRPs															42,000,000
68th Street Dump [Abstract]
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			100,000
Minimum additional GHG emissions by stationary sources after a modification			75,000
Asbestos Loss Contingency [Abstract]
Asbestos liability reserve															47,000,000		49,000,000
Asbestos liability reserve related to open claims															13,000,000
Open asbestos liability claims															172																																																																																				480
Asbestos liability reserve related to anticipated claims															34,000,000
Dividend Payments Restrictions [Abstract]
Preferred securities	87,000,000	87,000,000																																																																				87,000,000		87,000,000
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
US Department Of Energy Settlements [Abstract]
Percentage of ownership interest in CENG (as a percent)	50.01%														50.01%
FERC Settlement [Abstract]
FERC civil penalty															135,000,000
FERC disgorgement															110,000,000
FERC disgorement portion paid to each of six grid operators															1,000,000
Number of States in PJM	13
FERC settlement recorded in operation and maintenance expense															195,000,000
FERC settlement recorded as preacquisition contingency															50,000,000
Construction Commitments [Line Items]
Solar facility construction commitments																															443,000,000	445,000,000
Wind facility construction commitments															460,000,000
Megawatts of wind facility related to construction commitments															404
Energy Commitments Table [Abstract]
Due within one year															1,155,000,000									391,000,000	[7]	61,000,000	[8]	26,000,000	[9]	677,000,000
Due in second year															1,042,000,000									360,000,000	[7]	67,000,000	[8]	32,000,000	[9]	583,000,000
Due in third year															765,000,000									354,000,000	[7]	34,000,000	[8]	26,000,000	[9]	351,000,000
Due in fourth year															373,000,000									351,000,000	[7]	9,000,000	[8]	13,000,000	[9]
Due in fifth year															271,000,000									265,000,000	[7]	4,000,000	[8]	2,000,000	[9]
Thereafter															710,000,000									668,000,000	[7]	6,000,000	[8]	36,000,000	[9]
Total energy commitments															4,316,000,000									2,389,000,000	[7]	181,000,000	[8]	135,000,000	[9]	1,611,000,000
Utility Energy Purchase Commitments [Abstract]
Energy purchase commitments from third parties																																														1,182,000,000	[10]	95,000,000	[10]	367,000,000	[10]	309,000,000	[10]	134,000,000	[10]	137,000,000	[10]	140,000,000	[10]											1,208,000,000	[11]								675,000,000	[11]	416,000,000	[11]	93,000,000	[11]	24,000,000	[11]													1,299,000,000	[12]							646,000,000	[12]	544,000,000	[12]	109,000,000	[12]
Renewable energy credit purchase commitments																																																																						39,000,000									7,000,000		11,000,000		9,000,000		2,000,000		2,000,000	8,000,000
Long-term renewable energy and associated RECs																																														1,697,000,000	[13]	36,000,000	[13]	71,000,000	[13]	74,000,000	[13]	74,000,000	[13]	81,000,000	[13]	1,361,000,000	[13]
Curtailment Services																																																																						12,000,000									12,000,000																				144,000,000								31,000,000		49,000,000		46,000,000		18,000,000
Fuel And Natural Gas Purchase Obligations [Abstract]
Fuel Purchase Commitments															8,343,000,000			975,000,000	1,076,000,000	1,097,000,000	1,129,000,000	732,000,000	3,334,000,000																																															494,000,000			137,000,000	97,000,000	78,000,000	55,000,000	34,000,000	93,000,000																					656,000,000		85,000,000	84,000,000	70,000,000	52,000,000	51,000,000	314,000,000
Unrecorded Unconditional Purchase Obligation [Abstract]
Other Purchase Obligations, Due within One Year	525,000,000														308,000,000																															85,000,000																								60,000,000																													7,000,000
Other Purchase Obligations, Due within Two Years	167,000,000														99,000,000																															5,000,000																								18,000,000																													11,000,000
Other Purchase Obligations, Due within Three Years	127,000,000														90,000,000																																																							17,000,000
Other Purchase Obligations, Due within Four Years	87,000,000														67,000,000																																																							1,000,000
Other Purchase Obligations, Due within Five Years	25,000,000														5,000,000																																																							1,000,000
Other Purchase Obligations, Due after Five Years	112,000,000														28,000,000																																																							8,000,000
Other Purchase Obligations, Total	$ 1,043,000,000														$ 597,000,000																															$ 90,000,000																								$ 105,000,000																													$ 18,000,000

[1] Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties. As of March 31, 2012, guarantees of $1 million have been issued by Exelon to provide support for certain letters of credit as required by third parties.

[2] Primarily reflects guarantees of $200 million Trust Preferred Securities of ComEd Financing III.

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

[4] Primarily reflects guarantees of $250 million Trust Preferred Securities of BGE Capital Trust II.

[5] 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 nuclear insurance and credit support. The estimated net exposure for obligations under commercial transactions covered by these guarantees was $1.6 billion at March 31, 2012, which represents the total amount Exelon could be required to fund based on March 31, 2012 market prices.

[6] Primarily reflects guarantees issued to ensure performance under energy marketing and other specific contracts and $205 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 $0.3 billion at March 31, 2012, which represents the total amount Generation could be required to fund based on March 31, 2012 market prices.

[7] 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, 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.

[8] Excludes renewable energy PPA contracts that are contingent in nature.

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

[10] 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.

[11] 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.

[12] 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.

[13] 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. See Note 4 - Regulatory Matters for additional information.