Merger and Acquisitions (Details) (USD $)	3 Months Ended					6 Months Ended
	Jun. 30, 2013		Mar. 31, 2013	Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Finite Lived Intangible Assets Net [Abstract]
Amortization of Regulatory Asset	$ 19,000,000			$ 9,000,000		$ 38,000,000		$ 12,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	6,141,000,000			5,966,000,000		12,223,000,000		10,656,000,000
Net income	497,000,000			289,000,000		498,000,000		490,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Earnings Per Share, Basic								$ 1.26
Business Acquisition, Pro Forma Earnings Per Share, Diluted								$ 1.25
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Construction Time Frame						2 years
Business Acquisition, Gain (Loss) On Assets Sold	272,000,000					272,000,000
Business Acquisition, Gain (Loss) On Assets Sold Update						8,000,000
Business Acquisition Potential Cash Payment	40,000,000					40,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start			111,000,000			111,000,000
Severance Charges				42,000,000				109,000,000
Stock Compensation Expense				(5,000,000)				3,000,000
Other Expense Charges				(1,000,000)				7,000,000
Total Severance Benefits				36,000,000	[1]	3,000,000		119,000,000	[1]
Payments						37,000,000
Restructuring Reserve, Period End	77,000,000					77,000,000
Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Intercompany Allocation						2,000,000	[2]
One-time Termination Benefits [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Intercompany Allocation						1,000,000
Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Intercompany Allocation						1,000,000
Minimum [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Construction Cost	95,000,000					95,000,000
Maximum [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Construction Cost	120,000,000					120,000,000
Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	30,000,000			119,000,000		63,000,000		635,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets	4,936,000,000					4,936,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	9,342,000,000					9,342,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts	3,218,000,000					3,218,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships	457,000,000					457,000,000
Business Acquisition, Purchase Price Allocation, CENG Investment	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
Business Acquisition, Purchase Price Allocation, Assets Acquired	22,900,000,000					22,900,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities	3,408,000,000					3,408,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	4,683,000,000					4,683,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts	1,722,000,000					1,722,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt	5,632,000,000					5,632,000,000
Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value	90,000,000					90,000,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	15,535,000,000					15,535,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	7,365,000,000					7,365,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						10,000,000		41,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue				6,256,000,000				13,284,000,000
Business Acquisition, Pro Forma Net Income (Loss)				528,000,000				979,000,000
Business Acquisition, Pro Forma Earnings Per Share, Basic				$ 0.62
Business Acquisition, Pro Forma Earnings Per Share, Diluted				$ 0.62
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, Development Of New Generation Cost	625,000,000					625,000,000
Business Acquisition, Expected New Generation Development Time Frame						10 years
Constellation Energy Group Acquisition [Member] | Minimum [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Expected New Generation Mwh						285
Constellation Energy Group Acquisition [Member] | Maximum [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Expected New Generation Mwh						300
Exelon Generation Co L L C [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	4,070,000,000			3,765,000,000		7,603,000,000		6,508,000,000
Net income	328,000,000			165,000,000		310,000,000		332,000,000
Business Acquisition, Regulatory Matters [Abstract]
Lease Agreement Time Frame						20 years
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start			33,000,000			33,000,000
Severance Charges				29,000,000				64,000,000
Stock Compensation Expense				(3,000,000)				2,000,000
Other Expense Charges				(1,000,000)				4,000,000
Total Severance Benefits				25,000,000	[1]	3,000,000		70,000,000	[1]
Payments						13,000,000
Restructuring Reserve, Intercompany Allocation				10,000,000		3,000,000		40,000,000
Restructuring Reserve, Period End	20,000,000					20,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	20,000,000			94,000,000		43,000,000		204,000,000
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Current Assets	3,638,000,000					3,638,000,000
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	4,054,000,000					4,054,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Contracts	3,218,000,000					3,218,000,000
Business Acquisition, Purchase Price Allocation, Intangible Assets, Relationships	457,000,000					457,000,000
Business Acquisition, Purchase Price Allocation, CENG Investment	1,942,000,000					1,942,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Assets	1,266,000,000					1,266,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired	14,575,000,000					14,575,000,000
Business Acquisition, Purchase Price Allocation, Current Liabilities	2,804,000,000					2,804,000,000
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	1,933,000,000					1,933,000,000
Business Acquisition, Purchase Price Allocation, Liability Contracts	1,512,000,000					1,512,000,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Long-term Debt	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
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	9,311,000,000					9,311,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	5,264,000,000					5,264,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue				4,051,000,000				8,523,000,000
Business Acquisition, Pro Forma Net Income (Loss)				397,000,000				567,000,000
Exelon Generation Co L L C [Member] | Perryman Construction [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Construction Cost	89,000,000					89,000,000
Business Acquisition, Divesture Wattage						120
Commonwealth Edison Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	1,080,000,000			1,281,000,000		2,239,000,000		2,670,000,000
Net income	96,000,000			42,000,000		14,000,000		129,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start			1,000,000			1,000,000
Severance Charges				6,000,000	[3]			15,000,000	[3]
Stock Compensation Expense				(1,000,000)	[3]
Other Expense Charges				0	[3]			1,000,000	[3]
Total Severance Benefits				5,000,000	[1],[3]			16,000,000	[1],[3]
Restructuring Reserve, Intercompany Allocation				3,000,000				14,000,000
Restructuring Reserve, Period End	1,000,000					1,000,000
Merger related severance regulatory asset				5,000,000				16,000,000
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	5,000,000			8,000,000		9,000,000		26,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						8,000,000		23,000,000
PECO Energy Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	672,000,000			715,000,000		1,567,000,000		1,590,000,000
Net income	78,000,000			80,000,000		200,000,000		177,000,000
Restructuring Reserve [Roll Forward]
Severance Charges				4,000,000				7,000,000
Stock Compensation Expense				(1,000,000)
Other Expense Charges				(1,000,000)
Total Severance Benefits				2,000,000	[1]			7,000,000	[1]
Restructuring Reserve, Intercompany Allocation				2,000,000				7,000,000
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	2,000,000			4,000,000		5,000,000		11,000,000
Baltimore Gas and Electric Company [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	653,000,000			616,000,000		1,533,000,000		1,312,000,000
Revenues Impact	653,000,000			616,000,000		1,533,000,000		668,000,000
Net Income Loss Impact	25,000,000			16,000,000		106,000,000		(49,000,000)
Net income	25,000,000			16,000,000		106,000,000		(14,000,000)
Regulatory Assets Transfer Changes			6,000,000			8,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start			11,000,000			11,000,000
Severance Charges				3,000,000	[4]			17,000,000	[4]
Stock Compensation Expense				(1,000,000)	[4]
Other Expense Charges				0	[4]			1,000,000	[4]
Total Severance Benefits				2,000,000	[1],[4]			18,000,000	[1],[4]
Payments						3,000,000
Restructuring Reserve, Intercompany Allocation				1,000,000				6,000,000
Restructuring Reserve, Period End	8,000,000					8,000,000
Merger related severance regulatory asset				2,000,000				18,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member]
Business Acquisition Cost Of Acquired Entity [Abstract]
Business Combination, Integration Related Costs	1,000,000			2,000,000		3,000,000		171,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						2,000,000		18,000,000
Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	1,956,000,000					1,956,000,000
Finite lived intangible assets accumulated amortization	(1,334,000,000)					(1,334,000,000)
Finite lived intangible assets net	622,000,000					622,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	121,000,000					121,000,000
Future amortization expense in year two	118,000,000					118,000,000
Future amortizationExpense in year three	61,000,000					61,000,000
Future amortization expense in year four	13,000,000					13,000,000
Future amortization expense in year five	22,000,000					22,000,000
Future amortization expense in year six and thereafter						287,000,000
Customer Relationships [Member]
Finite Lived Intangible Assets Net [Abstract]
Amortization Of Contracts	4,000,000			6,000,000		9,000,000		7,000,000
Customer Relationships [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
Customer Relationships [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	214,000,000					214,000,000
Finite lived intangible assets accumulated amortization	(23,000,000)					(23,000,000)
Finite lived intangible assets net	191,000,000					191,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	10,000,000					10,000,000
Future amortization expense in year two	19,000,000					19,000,000
Future amortizationExpense in year three	19,000,000					19,000,000
Future amortization expense in year four	19,000,000					19,000,000
Future amortization expense in year five	19,000,000					19,000,000
Future amortization expense in year six and thereafter						105,000,000
Trade Names [Member]
Finite Lived Intangible Assets Net [Abstract]
Amortization Of Contracts	6,000,000			6,000,000		12,000,000		8,000,000
Trade Names [Member] | Constellation Energy Group Acquisition [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Finite Lived Intangible Asset Weighted Average Useful Life						10 years
Trade Names [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	243,000,000					243,000,000
Finite lived intangible assets accumulated amortization	(32,000,000)					(32,000,000)
Finite lived intangible assets net	211,000,000					211,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	12,000,000					12,000,000
Future amortization expense in year two	24,000,000					24,000,000
Future amortizationExpense in year three	24,000,000					24,000,000
Future amortization expense in year four	24,000,000					24,000,000
Future amortization expense in year five	24,000,000					24,000,000
Future amortization expense in year six and thereafter						103,000,000
Power Supply Contracts [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets net	52,000,000					52,000,000
Amortization Of Contracts	162,000,000			370,000,000		332,000,000		501,000,000
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						1 year 6 months 3 days
Power Supply Contracts [Member] | Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	1,499,000,000	[5]				1,499,000,000	[5]
Finite lived intangible assets accumulated amortization	(1,279,000,000)	[5]				(1,279,000,000)	[5]
Finite lived intangible assets net	220,000,000	[5]				220,000,000	[5]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	99,000,000	[5]				99,000,000	[5]
Future amortization expense in year two	75,000,000	[5]				75,000,000	[5]
Future amortizationExpense in year three	18,000,000	[5]				18,000,000	[5]
Future amortization expense in year four	(30,000,000)	[5]				(30,000,000)	[5]
Future amortization expense in year five	(21,000,000)	[5]				(21,000,000)	[5]
Future amortization expense in year six and thereafter						$ 79,000,000	[5]

[1] 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.

[2] Includes salary continuance and health and welfare severance benefits. Amounts represent ongoing severance plan benefits. Amounts also include one-time termination benefits of $1 million for Exelon as of June 30, 2013.

[3] ComEd established regulatory assets of $5 million and $16 million for severance benefits costs for the three and six months ended June 30, 2012, respectively. The majority of these costs are expected to be recovered over a five-year period.

[4] BGE established regulatory assets of $2 million and $18 million for severance benefits costs for the three and six months ended June 30, 2012, respectively. The majority of these costs are being recovered over a five-year period beginning in March 2013. (d) Primarily includes life insurance, employer payroll taxes, educational assistance and outplacement services.

[5] Includes the fair value of BGE's power and gas supply contracts of $52 million for which an offsetting regulatory asset was also recorded