Merger and Acquisitions (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended					6 Months Ended						3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended					3 Months Ended			6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			6 Months Ended					3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Mar. 31, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] One-time Termination Benefits [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] One-time Termination Benefits [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] MW	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Revenues [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Expenses [Member] Years	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Income [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Minimum [Member] MW	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Maximum [Member] MW	Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Common Stock [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member] Equity Awards [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2011 Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2011 Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Expenses [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Income [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Antelope Valley Acquisition [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member] Series of Individually Immaterial Business Acquisitions [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2011 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2011 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2011 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2011 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Jun. 30, 2011 Baltimore Gas and Electric Company [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Jun. 30, 2011 Baltimore Gas and Electric Company [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Maryland Public Service Commission [Member] Operating Income [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Revenues [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Maryland Public Service Commission [Member] Operating Expenses [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Constellation Energy Group Acquisition [Member]	Jun. 30, 2012 Customer Relationships [Member] Constellation Energy Group Acquisition [Member] Total Assets [Member] Years	Jun. 30, 2012 Trade Names [Member] Constellation Energy Group Acquisition [Member] Total Assets [Member] Years	Jun. 30, 2012 Power Supply Contracts [Member] Constellation Energy Group Acquisition [Member] Total Assets [Member] Years
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life																																																																																																																				11.8	10.0	1.5	[1]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross																																																																																																																			$ 1,925,000,000	$ 229,000,000	$ 243,000,000	$ 1,453,000,000	[1]
Finite lived intangible assets accumulated amortization																																																																																																																			(504,000,000)	(7,000,000)	(8,000,000)	(489,000,000)	[1]
Finite lived intangible assets net																																																																																																																			1,421,000,000	222,000,000	235,000,000	964,000,000	[1]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One																																																																																																																			513,000,000	15,000,000	17,000,000	481,000,000	[1]
Future Amortization Expense Year Two																																																																																																																			429,000,000	23,000,000	24,000,000	382,000,000	[1]
Future Amortization Expense Year Three																																																																																																																			116,000,000	22,000,000	24,000,000	70,000,000	[1]
Future Amortization Expense Year Four																																																																																																																			60,000,000	21,000,000	24,000,000	15,000,000	[1]
Future Amortization Expense Year Five																																																																																																																			12,000,000	21,000,000	24,000,000	(33,000,000)	[1]
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 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.
Business Acquisition, Date of Acquisition [Abstract]
Business Acquisition, Effective Date of Acquisition																																					March 12, 2012																												September 30, 2011
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs																																		111,000,000			584,000,000																							94,000,000			204,000,000																0	2,000,000									4,000,000	11,000,000																							2,000,000	154,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets																																		4,944,000,000			4,944,000,000																							3,649,000,000			3,649,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment																																		9,249,000,000			9,249,000,000																							3,930,000,000			3,930,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts																																		3,171,000,000			3,171,000,000																							3,171,000,000			3,171,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships																																		472,000,000			472,000,000																							472,000,000			472,000,000
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																																		2,644,000,000			2,644,000,000																							1,266,000,000			1,266,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired																																		23,162,000,000			23,162,000,000																							14,430,000,000			14,430,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities																																		3,409,000,000			3,409,000,000																							2,798,000,000			2,798,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities																																		4,537,000,000			4,537,000,000																							1,781,000,000			1,781,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts																																		1,718,000,000			1,718,000,000																							1,512,000,000			1,512,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt																																		6,038,000,000			6,038,000,000																							2,972,000,000			2,972,000,000
Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value																																		95,000,000			95,000,000																							95,000,000			95,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed																																		15,797,000,000			15,797,000,000																							9,158,000,000			9,158,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net																																		7,365,000,000			7,365,000,000																							5,272,000,000			5,272,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	5,954,000,000	4,496,000,000	10,640,000,000	9,451,000,000																																			3,753,000,000	2,455,000,000	6,492,000,000	5,098,000,000																									1,281,000,000	1,444,000,000	2,670,000,000	2,910,000,000											715,000,000	842,000,000	1,590,000,000	1,996,000,000							616,000,000	674,000,000	1,312,000,000	1,650,000,000																			616,000,000	668,000,000
Net Income Loss	289,000,000	621,000,000	490,000,000	1,290,000,000																																			165,000,000	443,000,000	332,000,000	938,000,000																									42,000,000	114,000,000	129,000,000	183,000,000											80,000,000	83,000,000	177,000,000	210,000,000							16,000,000	16,000,000	(14,000,000)	97,000,000																			16,000,000	(49,000,000)
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue																																		6,256,000,000	7,425,000,000	[2]	13,284,000,000	15,493,000,000																						4,051,000,000	4,782,000,000	[3]	8,523,000,000	9,789,000,000
Business Acquisition, Pro Forma Net Income (Loss)																																		528,000,000	401,000,000	[2]	979,000,000	644,000,000																						397,000,000	221,000,000	[3]	567,000,000	442,000,000
Business Acquisition, Pro Forma Earnings Per Share, Basic																																		$ 0.62	$ 0.47	[2]	$ 1.26	$ 0.76
Business Acquisition, Pro Forma Earnings Per Share, Diluted																																		$ 0.62	$ 0.47	[2]	$ 1.25	$ 0.76
Business Acquisition, Pro Forma Nonrecurring Cost																																		111,000,000			584,000,000																							94,000,000			204,000,000
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)		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.
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares																															187,450,000	[4]	11,300,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned																														7,365,000,000	7,294,000,000	[4]	71,000,000
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
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				328,500,000																															35,000,000																																																	139,000,000
Business Acquisition, Preacquisition Contingency, Divesture Wattage																						2,648
Business Acquisition, Estimated Proceeds, Assets Held For Sale																						400,000,000
Business Acquisition, Estimated Gain (Loss), Sale Of Assets Held For Sale																						(275,000,000)
Business Acquisition Preacquisition Contingency Component [Abstract]
Business Acquisition, Preacquisition Contingency, BGE Rate Credit																								113,000,000	[5]																																																																																					113,000,000	[5]
Business Acquisition Preacquisition Contingency Equity Contribution																																																																																																												66,000,000
Business Acquisition Preacquisition Contingency Rate Credit Per Customer																								100																																																																																						100
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																															35,000,000																																																							28,000,000
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
Business Acquisition, Preacquisition Contingency, Miscellaneous Taxes																							(2,000,000)																																																																																						(2,000,000)
Business Acquisition, Preacquisition Contingency, Expected Headquarters Cost																												95,000,000	120,000,000
Business Acquisition, Preacquisition Contingency, Expected New Generation Cost																							625,000,000
Business Acquisition, Preacquisition Contingency, Expected New Generation Mwh																												285	300
DOE Loan Receipt																																																											69,000,000
Restructuring Costs [Abstract]
Restructuring And Related Cost Expected Cost							121,000,000																																						72,000,000																												16,000,000														7,000,000										18,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start					83,000,000	0	0																																				16,000,000		0																										0		0												0		0								10,000,000		0
Restructuring Reserve, Period Expense					36,000,000	83,000,000	119,000,000	40,000,000	[6]	107,000,000	[6]	2,000,000	[7]	2,000,000	[7]	(5,000,000)	3,000,000	(1,000,000)	[8]	7,000,000	[8]																						25,000,000	[9]	70,000,000	[9]	12,000,000	[6]	27,000,000	[6]	1,000,000	1,000,000	1,000,000	[8]	2,000,000	[8]															5,000,000	[10],[9]	16,000,000	[10],[9]	2,000,000	[6]	2,000,000	[6]							2,000,000	[9]	7,000,000	[9]							2,000,000	[11],[9]	18,000,000	[11],[9]	1,000,000	[6]	11,000,000	[6]	1,000,000	[8]	1,000,000	[8]
Restructuring Reserve, Settled with Cash					(1,000,000)		(1,000,000)
Restructuring Reserve, Intercompany Allocation																																											10,000,000		40,000,000																										3,000,000		14,000,000												2,000,000		7,000,000								1,000,000		6,000,000
Restructuring Reserve, Period End					118,000,000	83,000,000	118,000,000																																				30,000,000		30,000,000																										2,000,000		2,000,000												0		0								12,000,000		12,000,000
Merger related regulatory asset																																																																									$ 16,000,000																								$ 18,000,000

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

[2] The amounts above include non-recurring costs directly related to the merger of $111 million and $584 million for the three and six months ended June 30, 2011, respectively.

[3] The amounts above include non-recurring costs directly related to the merger of $94 million and $204 million for the three and six months ended June 30, 2011, respectively.

[4] 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.

[5] 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.

[6] Includes salary continuance and health and welfare severance benefits. Amounts represent ongoing severance plan benefits.

[7] One-time termination benefits began to be recognized in the second quarter of 2012.

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

[9] The amounts above include $10 million and $40 million at Generation, $3 million and $14 million at ComEd, $2 million and $7 million at PECO, and $1 million and $6 million at BGE, for amounts billed by BSC through intercompany allocations for the three and six months ended June 30, 2012, respectively.

[10] ComEd established regulatory assets of $16 million, as of June 30, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.

[11] Consistent with MDPSC precedent, BGE established a regulatory asset of $18 million, as of June 30, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.