Merger and Acquisitions (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended									3 Months Ended			9 Months Ended			3 Months Ended			9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended			9 Months Ended				3 Months Ended			9 Months Ended			3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended			3 Months Ended	9 Months Ended					3 Months Ended	9 Months Ended					9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] One-time Termination Benefits [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] One-time Termination Benefits [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Common Stock [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Equity Awards [Member]	Sep. 30, 2012 Minimum [Member] MW Years	Sep. 30, 2012 Maximum [Member] Years MW	Sep. 30, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2011 Constellation Energy Group Acquisition [Member]		Sep. 30, 2012 Constellation Energy Group Acquisition [Member] Days MW	Sep. 30, 2011 Constellation Energy Group Acquisition [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member]		Sep. 30, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]		Sep. 30, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] One-time Termination Benefits [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] One-time Termination Benefits [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Stock Compensation Plan [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Constellation Energy Group Acquisition [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member] MW	Sep. 30, 2012 Commonwealth Edison Co [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 PECO Energy Co [Member]		Sep. 30, 2011 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]		Sep. 30, 2011 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 PECO Energy Co [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2011 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2011 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Severance [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Other Severance Charges [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Constellation Energy Group Acquisition [Member] Years	Sep. 30, 2012 Constellation Energy Group Acquisition [Member]	Sep. 30, 2012 Customer Relationships [Member] Constellation Energy Group Acquisition [Member] Total Assets [Member] Years	Sep. 30, 2012 Trade Names [Member] Constellation Energy Group Acquisition [Member] Total Assets [Member] Years	Sep. 30, 2012 Power Supply Contracts [Member]	Sep. 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																																																																																																12.4	10.0		1.5	[1]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross																																																																																															$ 1,953,000,000	$ 214,000,000	$ 243,000,000		$ 1,496,000,000	[1]
Finite lived intangible assets accumulated amortization																																																																																															(737,000,000)	(9,000,000)	(14,000,000)	(224,000,000)	(714,000,000)	[1]
Finite lived intangible assets net																																																																																															1,216,000,000	205,000,000	229,000,000		782,000,000	[1]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One																																																																																															285,000,000	8,000,000	10,000,000		267,000,000	[1]
Future Amortization Expense Year Two																																																																																															439,000,000	19,000,000	24,000,000		396,000,000	[1]
Future Amortization Expense Year Three																																																																																															119,000,000	19,000,000	24,000,000		76,000,000	[1]
Future Amortization Expense Year Four																																																																																															61,000,000	19,000,000	24,000,000		18,000,000	[1]
Future Amortization Expense Year Five																																																																																															12,000,000	19,000,000	24,000,000		(31,000,000)	[1]
Business Acquisition, Entity Acquired and Reason for Acquisition [Abstract]
Business Acquisitions, Megawatts Acquired																																																										230
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs		18,000,000		43,000,000																						87,000,000			671,000,000					5,000,000			6,000,000															79,000,000			283,000,000						2,000,000			2,000,000					0	2,000,000			4,000,000			1,000,000			3,000,000	13,000,000													1,000,000	155,000,000
Business Combination, Bargain Purchase [Abstract]
Business Combination, Bargain Purchase, Gain Recognized, Amount		36,000,000		36,000,000																														36,000,000			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																										9,240,000,000			9,240,000,000																							3,948,000,000			3,948,000,000
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																										2,668,000,000			2,668,000,000																							1,266,000,000			1,266,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired																										23,201,000,000			23,201,000,000																							14,469,000,000			14,469,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities																										3,431,000,000			3,431,000,000																							2,798,000,000			2,798,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities																										4,553,000,000			4,553,000,000																							1,837,000,000			1,837,000,000
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																										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																										92,000,000			92,000,000																							92,000,000			92,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed																										15,836,000,000			15,836,000,000																							9,211,000,000			9,211,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net																										7,365,000,000			7,365,000,000																							5,258,000,000			5,258,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	6,565,000,000	5,254,000,000	17,205,000,000	14,705,000,000																												4,017,000,000		2,821,000,000	10,509,000,000		7,919,000,000																						1,484,000,000		1,784,000,000	4,154,000,000		4,694,000,000							806,000,000		946,000,000	2,396,000,000		2,942,000,000					720,000,000		745,000,000	2,032,000,000		2,394,000,000
Revenues Impact																																																																																	720,000,000			1,388,000,000
Net Income Loss Impact																																																																																				(49,000,000)
Net income	297,000,000	602,000,000	787,000,000	1,892,000,000																												87,000,000		386,000,000	419,000,000		1,325,000,000																						90,000,000		112,000,000	219,000,000		295,000,000							123,000,000		105,000,000	300,000,000		314,000,000					0		2,000,000	(14,000,000)		99,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue																										6,841,000,000	8,219,000,000	[2]	20,084,000,000	23,839,000,000	[2]																					4,293,000,000	5,133,000,000	[3]	12,753,000,000	14,996,000,000	[3]
Business Acquisition, Pro Forma Net Income (Loss)																										492,000,000	379,000,000	[2]	1,439,000,000	1,119,000,000	[2]																					282,000,000	163,000,000	[3]	805,000,000	690,000,000	[4]
Business Acquisition, Pro Forma Earnings Per Share, Basic																										$ 0.58	$ 0.45	[2]	$ 1.79	$ 1.32	[2]
Business Acquisition, Pro Forma Earnings Per Share, Diluted																										$ 0.57	$ 0.44	[2]	$ 1.79	$ 1.31	[2]
Business Acquisition, Pro Forma Nonrecurring Cost																											74,000,000			242,000,000																							69,000,000			318,000,000
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement																										1,000,000,000			1,000,000,000
Business Acquisition, Costs Recognized Post Merger [Abstract]
Business Acquisition, Regulatory Rate Credit Per Customer																																																																																				100
BGE rate credit of $100 per residential customer			113,000,000																																																																																	113,000,000
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
Charitable contributions at $7 million per year for 10 years			70,000,000																																35,000,000																																																	28,000,000
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																								2	3
Business Acquisition, Development Of New Generation Cost																										625,000,000			625,000,000
Business Acquisition, Expected New Generation Mwh																								285	300
Business Acquisition, Expected New Generation Development Time Frame																																																																																														10
Business Acquisition, Divesture Wattage																													2,648
Business Acquisition, Divesture Sales Days																													150
Business Acquisition, Divesture Sales Days Extension																													30
Business Acquisition, Proceeds Assets Held For Sale	356,000,000		356,000,000																							366,000,000			366,000,000
Business Acquisition, Gain (Loss) On Sale Of Assets Held For Sale	(278,000,000)		(278,000,000)																							(268,000,000)			(268,000,000)
Business Acquisition, Fair Value of Assets Held For Sale	339,000,000		339,000,000
DOE Loan Receipt																																																										69,000,000
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
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
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start						118,000,000	0																																			30,000,000	0																						2,000,000	0											0	0									12,000,000	0
Severance Charges	8,000,000		117,000,000																													4,000,000			68,000,000																								1,000,000			16,000,000	[5]								1,000,000			8,000,000							1,000,000			18,000,000	[6]
Stock Compensation Expense	3,000,000		6,000,000																													2,000,000			4,000,000																								1,000,000			1,000,000	[5]
Other Expense Charges			7,000,000																																4,000,000																											1,000,000	[5]																					1,000,000	[6]
Total Severance Benefits	11,000,000		130,000,000																													6,000,000	[7]		76,000,000	[7]																							2,000,000	[7]		18,000,000	[5],[7]								1,000,000	[7]		8,000,000	[7]						1,000,000	[7]		19,000,000	[6],[7]
Restructuring Reserve, Period Expense					83,000,000			7,000,000	[8]	114,000,000	[8]	1,000,000	[9]	3,000,000	[9]	3,000,000	6,000,000	7,000,000	[10]																			1,000,000	[4]	1,000,000	[5]			4,000,000	[8]	31,000,000	[8]	1,000,000	2,000,000	2,000,000	[10]																2,000,000	[8]																					11,000,000	[8]	1,000,000	[10]
Payments						9,000,000	10,000,000																									2,000,000			2,000,000																																														1,000,000			1,000,000
Restructuring Reserve, Intercompany Allocation																																										0	40,000,000																						2,000,000	16,000,000											1,000,000	8,000,000									1,000,000	7,000,000
Restructuring Reserve, Period End						120,000,000	120,000,000																																			34,000,000	34,000,000																						2,000,000	2,000,000											0	0									11,000,000	11,000,000
Merger related regulatory asset																																																																		34,000,000																						22,000,000
Merger related severance regulatory asset																																																																		$ 18,000,000																						$ 19,000,000

[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 $74 million and $242 million for the three and nine months ended September 30, 2011, respectively.

[3] The amounts above include non-recurring costs directly related to the merger of $69 million and $318 million for the three and nine months ended September 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] ComEd established regulatory assets of $18 million, as of September 30, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.

[6] Consistent with MDPSC precedent, BGE established a regulatory asset of $19 million, as of September 30, 2012, for severance benefits costs. The majority of these costs are expected to be recovered over a five-year period.

[7] The amounts above include $0 million and $40 million at Generation, $2 million and $16 million at ComEd, $1 million and $8 million at PECO, and $1 million and $7 million at BGE, for amounts billed by BSC through intercompany allocations for the three and nine months ended September 30, 2012, respectively.

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

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

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