Merger and Acquisitions (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Contingent consideration at fair value	$ (7,365,000,000)
Business Acquisition, Impact Of Merger [Abstract]
Revenues	4,686,000,000		4,956,000,000
Net Income Loss	200,000,000		669,000,000
Earnings Per Share, Basic	$ 0.28		$ 1.01
Earnings Per Share, Diluted	$ 0.28		$ 1.01
Constellation Energy Group Acquisition [Member]
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost	91,000,000
Restructuring and Related Cost, Incurred Cost	83,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	83,000,000	[1]
Constellation Energy Group Acquisition [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	67,000,000	[1],[2]
Constellation Energy Group Acquisition [Member] | Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	8,000,000	[1]
Constellation Energy Group Acquisition [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	8,000,000	[1],[3]
Constellation Energy Group Acquisition [Member]
Business Acquisition, Preacquisition Contingency [Abstract]
Business Acquisition, Preacquisition Contingency, Divesture Wattage	2,648
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member]
Business Acquisition, Preacquisition Contingency [Abstract]
Business Acquisition, Preacquisition Contingency, Description of Settlement	In December 2011, Exelon and Constellation reached a settlement with the State of Maryland and the City of Baltimore and other interested parties in connection with the regulatory proceedings related to the merger that were pending before the MDPSC. As part of this settlement and the application for approval of the merger by MDPSC, Exelon agreed to provide a package of benefits to BGE customers, the City of Baltimore and the State of Maryland, resulting in an estimated direct investment in the State of Maryland of more than $1 billion.
Business Acquisition, Preacquisition Contingency, Amount of Settlement	1,000,000,000
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Expected New Generation Cost	625,000,000
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Revenues [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, BGE Rate Credit	113,000,000	[4]
Business Acquisition Preacquisition Contingency Rate Credit Per Customer	100
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Expenses [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Customer Investment Fund	113,500,000
Business Acquisition, Preacquisition Contingency, Contribution Renewable Energy	2,000,000
Business Acquisition, Preacquisition Contingency, Charitable Contributions	70,000,000
Business Acquisition Preacquisition Contingency Contributions Per Year	7,000,000
Business Acquisition Preacquisition Contingency Contributions Number Of Years	10
Business Acquisition, Preacquisition Contingency, Wind Development	32,000,000
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Income [Member]
Business Acquisition, Preacquisition Contingency [Abstract]
Business Acquisition, Preacquisition Contingency, Amount of Settlement	330,500,000
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Minimum [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Expected Headquarters Cost	95,000,000
Business Acquisition, Preacquisition Contingency, Expected New Generation Mwh	285
Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Maximum [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Expected Headquarters Cost	120,000,000
Business Acquisition, Preacquisition Contingency, Expected New Generation Mwh	300
Constellation Energy Group Acquisition [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	7,365,000,000
Business Acquisition, Equity Interest Issued Or Issuable, Exchange Ratio	0.930
Constellation Energy Group Acquisition [Member] | Common Stock [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Basis for Determining Value	Issuance of Exelon common stock to Constellation shareholders and equity award holders at the exchange ratio of 0.930 shares for each share of Constellation common stock; based on the opening price of Exelon common stock on March 12, 2012 of $38.91 (a)
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	187,450,000	[5]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	7,294,000,000	[5]
Business Acquisition, Equity Interest Issued or Issuable, Stock Price	38.91
Business Acquisition, Equity Interest Issued Or Issuable, Stock Withheld	700,000
Constellation Energy Group Acquisition [Member] | Equity Awards [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Basis for Determining Value	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-Sholes model.
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	11,300,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	71,000,000
Constellation Energy Group Acquisition [Member]
Business Acquisition, Date of Acquisition [Abstract]
Business Acquisition, Effective Date of Acquisition	March 12, 2012
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	484,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets	4,944,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	9,295,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts	3,624,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships	456,000,000
Business Acquisition, Purchase Price Allocation, CENG Investment	2,067,000,000
Business Acquisition, Purchase Price Allocation, Pension Regulatory Asset	740,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Assets	2,612,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired	23,738,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities	3,480,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	4,908,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts	2,268,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt	5,632,000,000
Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value	85,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	16,373,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	7,365,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue	6,864,000,000		8,002,000,000
Business Acquisition, Pro Forma Net Income (Loss)	112,000,000		593,000,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.13		$ 0.70
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.13		$ 0.70
Business Acquisition, Pro Forma Transaction Cost	144,000,000		0
Business Acquisition, Pro Forma Integration Related Cost	0
Business Acquisition, Pro Forma Preacquisition Settlement Cost	328,000,000
Exelon Generation Co L L C [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Contingent consideration at fair value	(5,272,000,000)
Business Acquisition, Impact Of Merger [Abstract]
Revenues	2,739,000,000		2,643,000,000
Net Income Loss	166,000,000		495,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member]
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost	51,000,000
Restructuring and Related Cost, Incurred Cost	45,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	45,000,000	[1]
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	35,000,000	[1],[2]
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member] | Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	5,000,000	[1]
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	5,000,000	[1],[3]
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Expenses [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Charitable Contributions	35,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Income [Member]
Business Acquisition, Preacquisition Contingency [Abstract]
Business Acquisition, Preacquisition Contingency, Amount of Settlement	35,000,000
Exelon Generation Co L L C [Member] | Antelope Valley Acquisition [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
DOE Loan Receipt	69,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	110,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets	3,649,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	3,993,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts	3,624,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships	456,000,000
Business Acquisition, Purchase Price Allocation, CENG Investment	2,067,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Assets	1,210,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired	14,999,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities	2,866,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	1,742,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts	2,062,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt	2,972,000,000
Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value	85,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	9,727,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	5,272,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue	3,997,000,000		4,873,000,000
Business Acquisition, Pro Forma Net Income (Loss)	67,000,000		343,000,000
Business Acquisition, Pro Forma Transaction Cost	75,000,000
Business Acquisition, Pro Forma Preacquisition Settlement Cost	35,000,000
Exelon Generation Co L L C [Member] | Antelope Valley Solar Ranch One Acquisition [Member]
Business Acquisition, Entity Acquired and Reason for Acquisition [Abstract]
Business Acquisition, Description of Acquired Entity	On September 30, 2011, Generation acquired all of the interests in Antelope Valley Solar Ranch One (Antelope Valley), a 230-MW solar PV project under development in northern Los Angeles County, California, from First Solar, Inc., which developed and will build, operate and maintain the project.
Business Acquisition, Date of Acquisition [Abstract]
Business Acquisition, Effective Date of Acquisition	September 30, 2011
Exelon Generation Co L L C [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition, Entity Acquired and Reason for Acquisition [Abstract]
Business Combination, Reason for Business Combination	Wind Development. As part of its plan to construct multiple wind facilities in 2012, Generation has acquired several project entities.  The acquisitions are not considered material individually or in the aggregate for disclosure.
Commonwealth Edison Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	1,388,000,000		1,466,000,000
Net Income Loss	87,000,000		69,000,000
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member]
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost	12,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	11,000,000	[1],[6]
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	9,000,000	[1],[2],[6]
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member] | Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1],[6]
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1],[3],[6]
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	2,000,000
PECO Energy Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	875,000,000		1,153,000,000
Net Income Loss	97,000,000		126,000,000
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member]
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost	6,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	5,000,000	[1]
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	3,000,000	[1],[2]
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member] | Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1]
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1],[3]
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	7,000,000
Baltimore Gas and Electric Company [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	696,000,000		976,000,000
Net Income Loss	(30,000,000)		81,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member]
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost	16,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	16,000,000	[1],[7]
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	14,000,000	[1],[2],[7]
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member] | Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1],[7]
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Expense	1,000,000	[1],[3],[7]
Baltimore Gas and Electric Company [Member] | Maryland Public Service Commission [Member] | Operating Income [Member]
Business Acquisition, Preacquisition Contingency [Abstract]
Business Acquisition, Preacquisition Contingency, Amount of Settlement	141,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition Preacquisition Contingency Future Equity Contribution	66,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Revenues [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, BGE Rate Credit	113,000,000	[4]
Business Acquisition Preacquisition Contingency Rate Credit Per Customer	100
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member] | Maryland Public Service Commission [Member] | Operating Expenses [Member]
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, Charitable Contributions	28,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	152,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	52,000,000
Net Income Loss	(65,000,000)
Constellation Energy Group Acquisition [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	1,812,000,000
Finite lived intangible assets accumulated amortization	(125,000,000)
Finite lived intangible assets net	1,687,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One	845,000,000
Future Amortization Expense Year Two	385,000,000
Future Amortization Expense Year Three	96,000,000
Future Amortization Expense Year Four	61,000,000
Future Amortization Expense Year Five	18,000,000
Customer Relationships [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life	11.8
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	213,000,000
Finite lived intangible assets accumulated amortization	(1,000,000)
Finite lived intangible assets net	212,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One	19,000,000
Future Amortization Expense Year Two	21,000,000
Future Amortization Expense Year Three	20,000,000
Future Amortization Expense Year Four	19,000,000
Future Amortization Expense Year Five	19,000,000
Trade Names [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life	10.0
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	243,000,000
Finite lived intangible assets accumulated amortization	(2,000,000)
Finite lived intangible assets net	241,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One	22,000,000
Future Amortization Expense Year Two	24,000,000
Future Amortization Expense Year Three	24,000,000
Future Amortization Expense Year Four	24,000,000
Future Amortization Expense Year Five	24,000,000
Power Supply Contracts [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life	1.5
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	1,356,000,000
Finite lived intangible assets accumulated amortization	(122,000,000)
Finite lived intangible assets net	1,234,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One	804,000,000
Future Amortization Expense Year Two	340,000,000
Future Amortization Expense Year Three	52,000,000
Future Amortization Expense Year Four	18,000,000
Future Amortization Expense Year Five	$ (25,000,000)

[1] For Generation, ComEd, PECO and BGE, amounts include charges billed through intercompany allocations.

[2] Includes salary continuance and health and welfare severance benefits. For the three months ended March 31, 2012, amounts represent ongoing severance plan benefits. One-time termination benefits are expected to begin to be recognized in the second quarter of 2012.

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

[4] Exelon will make 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.

[5] 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.

[6] Pursuant to EIMA, ComEd established a regulatory asset of $11 million for severance benefits costs, which are expected to be recovered over a five-year period.

[7] Consistent with prior MDPSC precedent, BGE established a regulatory asset of $16 million for severance benefits costs, and these costs are expected to be recovered over a five-year period.