Merger and Acquisitions (Details) (USD $)	3 Months Ended								12 Months Ended											0 Months Ended	12 Months Ended									12 Months Ended					3 Months Ended								12 Months Ended						12 Months Ended											9 Months Ended	12 Months Ended		3 Months Ended								12 Months Ended								3 Months Ended								12 Months Ended						3 Months Ended								12 Months Ended														12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 Severance [Member]		Dec. 31, 2012 One-time Termination Benefits [Member]	Dec. 31, 2012 Stock Compensation Plan [Member]	Dec. 31, 2012 Other Severance Charges [Member]		Nov. 30, 2012 Constellation Energy Group Acquisition [Member] Common Stock [Member]	Dec. 31, 2012 Constellation Energy Group Acquisition [Member] Common Stock [Member]		Dec. 31, 2012 Constellation Energy Group Acquisition [Member] Equity Awards [Member]		Dec. 31, 2012 Minimum [Member] MW	Dec. 31, 2012 Maximum [Member] MW	Dec. 31, 2012 Constellation Energy Group Acquisition [Member] MW	Dec. 31, 2011 Constellation Energy Group Acquisition [Member]	Nov. 30, 2012 Constellation Energy Group Acquisition [Member]	Dec. 31, 2011 Wolf Hollow Acquisition [Member]	Dec. 31, 2011 Antelope Valley Solar Ranch One Acquisition [Member]		Dec. 31, 2010 Exelon Wind Acquisition [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]	Apr. 05, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Severance [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] One-time Termination Benefits [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Stock Compensation Plan [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Other Severance Charges [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Wolf Hollow Acquisition [Member] MW	Dec. 31, 2012 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member] NumberOfHomes SolarPanels	Dec. 31, 2011 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member] MW	Sep. 30, 2011 Exelon Generation Co L L C [Member] Exelon Wind Acquisition [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Exelon Wind Acquisition [Member] MW	Dec. 31, 2010 Exelon Generation Co L L C [Member] Exelon Wind Acquisition [Member] MW	Dec. 31, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member]	Jun. 30, 2011 Commonwealth Edison Co [Member]	Mar. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Severance [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Mar. 31, 2012 PECO Energy Co [Member]	Dec. 31, 2011 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member]	Jun. 30, 2011 PECO Energy Co [Member]	Mar. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member]		Dec. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2011 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member]	Sep. 30, 2011 Baltimore Gas and Electric Company [Member]	Jun. 30, 2011 Baltimore Gas and Electric Company [Member]	Mar. 31, 2011 Baltimore Gas and Electric Company [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] Severance [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Other Severance Charges [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Customer Relationships [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Trade Names [Member] Constellation Energy Group Acquisition [Member]	Dec. 31, 2012 Power Supply Contracts [Member]	Dec. 31, 2012 Power Supply Contracts [Member] Constellation Energy Group Acquisition [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life																																																																																																																12 years 4 months 26 days	10 years		1 year 6 months 3 days	[1]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	$ 576,000,000								$ 576,000,000																																																																																																						$ 1,953,000,000	$ 214,000,000	$ 243,000,000		$ 1,496,000,000	[1]
Finite lived intangible assets accumulated amortization	(132,000,000)								(132,000,000)																																																																																																						(1,017,000,000)	(15,000,000)	(20,000,000)		(982,000,000)	[1]
Finite lived intangible assets net	444,000,000								444,000,000																																																																																																						936,000,000	199,000,000	223,000,000		514,000,000	[1]
Amortization Of Contracts																																																																																																															1,098,000,000
Amortization of Regulatory Asset																																																																																																																		116,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	28,000,000								28,000,000																																																																																																						437,000,000	19,000,000	24,000,000		394,000,000	[1]
Future amortization expense in year two	29,000,000								29,000,000																																																																																																						117,000,000	19,000,000	24,000,000		74,000,000	[1]
Future mortizationExpense in year three	29,000,000								29,000,000																																																																																																						62,000,000	19,000,000	24,000,000		19,000,000	[1]
Future amortization expense in year four	29,000,000								29,000,000																																																																																																						12,000,000	19,000,000	24,000,000		(31,000,000)	[1]
Future amortization expense in year five	29,000,000								29,000,000																																																																																																						21,000,000	19,000,000	24,000,000		(22,000,000)	[1]
Future amortization expense in year six and thereafter																																																																																																															287,000,000	104,000,000	103,000,000		80,000,000	[1]
Business Acquisition, Entity Acquired and Reason for Acquisition [Abstract]
Business Acquisitions, Megawatts Acquired																																																									720		230			735
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs																											746,000,000	77,000,000																											340,000,000	15,000,000																						5,000,000													17,000,000	2,000,000																		160,000,000
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Business Acquisition Cost Of Acquired Entity Cash Paid																														305,000,000	75,000,000		893,000,000
Business Acquisition, Preexisting Relationship, Gain (Loss) Recognized																														6,000,000
Contingent consideration at fair value													(32,000,000)																																		(32,000,000)
Escrow Deposit																																	32,000,000
Total fair value of consideration recorded																														311,000,000	75,000,000		925,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net Abstract
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment																														347,000,000	15,000,000		700,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory																														5,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Intangibles																															190,000,000	[2]	224,000,000	[2]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities																															135,000,000	[3]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Non-Controlling Interest																																	(3,000,000)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Asset Retirment Obligations																																	(13,000,000)
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Working Capital																														(5,000,000)			18,000,000
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Assets And Liabilities																															5,000,000		(1,000,000)
Total net identifiable assets																														347,000,000	75,000,000		925,000,000
Expected Investment In Equity																																																										701,000,000
DOE advances received																																			219,000,000								219,000,000					69,000,000										69,000,000
DOE loan guarantee																																											646,000,000															646,000,000
Amount of solar panels																																																										3,800,000
Amount of homes powered by electricity generated																																																										75,000
Purchased Power agreement time																																																										25 years
Contingent consideration potential cash payment																																																													40,000,000
Contingent consideration paid																																																												16,000,000
Acquisition of John Deere Renewables additional wind projects in advance stages of development capacity																																																													230
Probability of project to be constructed																																																												100.00%
Contingent consideration recorded in operation and maintenance expense																																																													2,000,000
Contingent consideration recorded in current liabilities																																																													10,000,000
Contingent consideration recorded in deferred credits																																																													8,000,000
Footnotes To Business Combination Recognized Identifiable Assets Acquired Liabilities Assumed Net [Abstract]
First Solar Corporation Payable																																																										87,000,000	135,000,000
Business Combination, Bargain Purchase [Abstract]
Business Combination, Bargain Purchase, Gain Recognized, Amount																														36,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets	4,936,000,000								4,936,000,000																										3,638,000,000								3,638,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	9,342,000,000								9,342,000,000																										4,054,000,000								4,054,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts	3,218,000,000								3,218,000,000																										3,218,000,000								3,218,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships	457,000,000								457,000,000																										457,000,000								457,000,000
Business Acquisition, Purchase Price Allocation, CENG Investment	1,942,000,000								1,942,000,000																										1,942,000,000								1,942,000,000
Business Acquisition, Purchase Price Allocation, Pension Regulatory Asset	740,000,000								740,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Assets	2,265,000,000								2,265,000,000																										1,266,000,000								1,266,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired	22,900,000,000								22,900,000,000																										14,575,000,000								14,575,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities	3,408,000,000								3,408,000,000																										2,804,000,000								2,804,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	4,683,000,000								4,683,000,000																										1,933,000,000								1,933,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts	1,722,000,000								1,722,000,000																										1,512,000,000								1,512,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt	5,632,000,000								5,632,000,000																										2,972,000,000								2,972,000,000
Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value	90,000,000								90,000,000																										90,000,000								90,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	15,535,000,000								15,535,000,000																										9,311,000,000								9,311,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	7,365,000,000								7,365,000,000																										5,264,000,000								5,264,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	6,284,000,000	6,565,000,000	5,954,000,000	4,686,000,000	4,357,000,000	5,254,000,000	4,496,000,000	4,956,000,000	23,489,000,000		19,063,000,000		18,644,000,000																						3,928,000,000	4,017,000,000	3,753,000,000	2,739,000,000	2,528,000,000	2,821,000,000	2,455,000,000	2,643,000,000	14,437,000,000		10,447,000,000		10,025,000,000																1,290,000,000	1,484,000,000	1,281,000,000	1,388,000,000	1,362,000,000	1,784,000,000	1,444,000,000	1,466,000,000	5,443,000,000		6,056,000,000	6,204,000,000					790,000,000	806,000,000	715,000,000	875,000,000	778,000,000	946,000,000	842,000,000	1,153,000,000	3,186,000,000		3,720,000,000	5,519,000,000			703,000,000	720,000,000	616,000,000	696,000,000	673,000,000	745,000,000	674,000,000	976,000,000	2,735,000,000		3,068,000,000	3,541,000,000
Revenues Impact																																																																																																					2,091,000,000
Net Income Loss Impact																																																																																																					(31,000,000)
Net income	378,000,000	296,000,000	286,000,000	200,000,000	606,000,000	601,000,000	620,000,000	668,000,000	1,171,000,000		2,499,000,000		2,563,000,000																						137,000,000	91,000,000	166,000,000	168,000,000	447,000,000	386,000,000	443,000,000	495,000,000	558,000,000		1,771,000,000		1,972,000,000																160,000,000	90,000,000	42,000,000	87,000,000	121,000,000	112,000,000	114,000,000	69,000,000	379,000,000		416,000,000	337,000,000					79,000,000	122,000,000	79,000,000	96,000,000	73,000,000	104,000,000	82,000,000	125,000,000	381,000,000		389,000,000	324,000,000			15,000,000	(4,000,000)	13,000,000	(33,000,000)	34,000,000	(2,000,000)	13,000,000	78,000,000	4,000,000		136,000,000	147,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue									26,700,000,000		30,712,000,000	[4]																															17,013,000,000		19,494,000,000	[5]
Business Acquisition, Pro Forma Net Income (Loss)									2,092,000,000		974,000,000	[4]																															1,205,000,000		324,000,000	[5]
Business Acquisition, Pro Forma Earnings Per Share, Basic									$ 2.56		$ 1.15	[4]
Business Acquisition, Pro Forma Earnings Per Share, Diluted									$ 2.55		$ 1.14	[4]
Business Acquisition, Pro Forma Nonrecurring Cost											236,000,000																																		203,000,000
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement																											1,000,000,000
Business Acquisition, Costs Recognized Post Merger [Abstract]
Business Acquisition, Regulatory Rate Credit Per Customer																																																																																																					100
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
BGE rate credit of $100 per residential customer									113,000,000	[6]																																																																																											113,000,000	[6]
Charitable contributions at $7 million per year for 10 years									70,000,000																																		35,000,000																																																										28,000,000
Length of years for charitable contributions at $7 million per year									10 years
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 Charitable Contributions Per Year									7,000,000
Business Acquisition, Costs Recognized Post Merger Footnotes [Abstract]
Business Acquisition, Equity Contribution																																																																																																					66,000,000
Business Acquisition, Construction Cost																									95,000,000	120,000,000
Business Acquisition, Construction Time Frame																									1 year	2 years
Business Acquisition, Development Of New Generation Cost																											625,000,000
Business Acquisition, Expected New Generation Mwh																									285	300
Business Acquisition, Expected New Generation Development Time Frame									10 years
Business Acquisition, Divesture Wattage																											2,648
Business Acquisition, Divesture Sales Days									150 days
Business Acquisition, Divesture Sales Days Extension									30 days
Business Acquisition, Proceeds Assets Held For Sale																													371,000,000
Business Acquisition, Gain (Loss) On Sale Of Assets Held For Sale																													278,000,000
Business Acquisition, Gain (Loss) On Sale Of Assets Held For Sale Update																													272,000,000
Business Acquisition Potential Cash Payment	40,000,000								40,000,000
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares																					187,450,000	[7]	11,300,000	[8]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned																					7,294,000,000	[7]	71,000,000	[8]
Business Acquisition, Equity Interest Issued Or Issuable, Exchange Ratio																					0.930
Business Acquisition, Equity Interest Issued or Issuable, Stock Price																					38.91
Business Acquisition, Equity Interest Issued Or Issuable, Stock Withheld																				700,000
Restructuring Reserve [Roll Forward]
Severance Charges									124,000,000	[9]				124,000,000	[10]																												80,000,000	[9]					38,000,000	[10]																					14,000,000	[11],[9]			2,000,000	[10]											7,000,000	[9]													17,000,000	[12],[9]			11,000,000	[10]
Stock Compensation Expense									7,000,000	[9]							7,000,000																										4,000,000	[9]								2,000,000																			1,000,000	[11],[9]																													1,000,000	[12],[9]
Other Expense Charges									7,000,000	[9]								7,000,000	[13]																								4,000,000	[9]									2,000,000	[13]																	1,000,000	[11],[9]																													1,000,000	[12],[9]					1,000,000	[13]
Total Severance Benefits									138,000,000	[9]																																	88,000,000	[9]																											16,000,000	[11],[9]															7,000,000	[9]													19,000,000	[12],[9]
Restructuring Reserve, Period Expense																3,000,000																																			1,000,000
Payments									27,000,000																																		9,000,000																												1,000,000																														1,000,000
Restructuring Reserve, Intercompany Allocation																																											46,000,000																												14,000,000																7,000,000														7,000,000
Restructuring Reserve, Period End	111,000,000								111,000,000																										33,000,000								33,000,000																				1,000,000								1,000,000																						11,000,000								11,000,000
Merger related regulatory asset																																																																													36,000,000																																22,000,000
Merger related severance regulatory asset																																																																							$ 16,000,000																														$ 19,000,000

[1] (a) Includes the fair value of BGE's power and gas supply contracts for which an offsetting Exelon Corporate regulatory asset was also recorded.

[2] See Note 8 - Intangible Assets for additional information.

[3] Generation concluded that the remaining, yet-to-be paid $135 million in consideration was embedded in the amounts payable under the Engineering, Procurement, Construction (EPC) agreement for First Solar, Inc. to construct the solar facility. For accounting purposes, this aspect of the transaction is considered to be akin to a "seller financing" arrangement. As such, Generation recorded a liability of $135 million associated with the portion of the future payments to First Solar, Inc. under the EPC agreement to reflect Generation's implicit amounts due First Solar, Inc. for the remainder of the value of the net assets acquired. The $135 million payable to First Solar, Inc. will be relieved as Generation makes payments for costs incurred over the project construction period. At December 31, 2012, $87 million remained payable to First Solar, Inc.

[4] The amounts above include non-recurring costs directly related to the merger of $236 million for the year ended December 31, 2011.

[5] The amounts above include non-recurring costs directly related to the merger of $203 million for the year ended December 31, 2011.

[6] 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.

[7] The number of shares issued excludes 0.7 million shares of stock that are held in a custodian account specifically for the settlement of unvested share-based restricted stock awards. The related share value is excluded from the estimated fair value as these awards have not vested and, therefore, are not in the purchase price.

[8] Includes vested Constellation stock options and restricted stock units converted at fair value to Exelon awards on March 12, 2012. The fair value of the stock options was determined using the Black-Scholes model.

[9] The amounts above include $46 million at Generation, $14 million at ComEd, $7 million at PECO, and $7 million at BGE, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2012.

[10] Includes salary continuance and health and welfare severance benefits. Amounts represent ongoing severance plan benefits. Amounts also include one-time termination benefits of $3 million and $1 million for Exelon and Generation, respectively, which they began to recognize in the second quarter of 2012.

[11] ComEd established regulatory assets of $16 million, as of December 31, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.

[12] Consistent with MDPSC precedent, BGE established a regulatory asset of $19 million, as of December 31, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.

[13] Primarily includes life insurance, employer payroll taxes, educational assistance, and outplacement services.