Merger and Acquisitions (Details) (USD $)	3 Months Ended					9 Months Ended
	Sep. 30, 2013		Mar. 31, 2013	Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Finite Lived Intangible Assets Net [Abstract]
Amortization of Regulatory Asset	$ 19,000,000			$ 36,000,000		$ 57,000,000		$ 80,000,000
Payments To Acquire Businesses Net Of Cash Acquired [Abstract]
Payments To Acquire Businesses Gross								0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net Abstract
Total assets	22,900,000,000					22,900,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	6,502,000,000	[1]		6,579,000,000	[1]	18,725,000,000	[2]	17,235,000,000	[2]
Net income	736,000,000			297,000,000		1,235,000,000		787,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Earnings Per Share, Basic								$ 1.79
Business Acquisition, Pro Forma Earnings Per Share, Diluted								$ 1.79
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	3,000,000			8,000,000		6,000,000		117,000,000
Non-Merger Severance Costs								120,000,000
Stock Compensation Expense				3,000,000				6,000,000
Other Expense Charges								7,000,000
Total Severance Benefits				11,000,000	[3]			130,000,000	[3]
Payments						52,000,000
Restructuring Reserve, Period End	65,000,000					65,000,000
Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Intercompany Allocation						5,000,000	[4]
Stock Compensation Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Intercompany Allocation						1,000,000
Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Severance Charges	12,000,000			5,000,000		14,000,000		11,000,000
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]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	43,000,000			95,000,000		106,000,000		729,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net Abstract
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment	9,342,000,000					9,342,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Asset Retirment Obligations	740,000,000					740,000,000
Current Assets	4,936,000,000					4,936,000,000
Unamortized Energy Contracts	3,218,000,000					3,218,000,000
Other intangibles, trade name and retail relationships	457,000,000					457,000,000
Investment in affiliates	1,942,000,000					1,942,000,000
Other assets	2,265,000,000					2,265,000,000
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract
Current liabilities	3,408,000,000					3,408,000,000
Unamortized energy contracts	1,722,000,000					1,722,000,000
Long-term debt, including current maturities	5,632,000,000					5,632,000,000
Business Combination Aquisition Of Less than 100 Percent Noncontrolling Interest Fair Value	90,000,000					90,000,000
Deferred credits and other liabilities and preferred securities	4,683,000,000					4,683,000,000
Total liabilities,preferred securities and noncontrolling Interest	15,535,000,000					15,535,000,000
Total purchase price	7,365,000,000					7,365,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						15,000,000		49,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue				6,841,000,000				20,084,000,000
Business Acquisition, Pro Forma Net Income (Loss)				492,000,000				1,439,000,000
Business Acquisition, Pro Forma Earnings Per Share, Basic				$ 0.58
Business Acquisition, Pro Forma Earnings Per Share, Diluted				$ 0.57
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]
Payments To Acquire Businesses Net Of Cash Acquired [Abstract]
Payments To Acquire Businesses Gross								0
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net Abstract
DOE loan guarantee						646,000,000
Total assets	14,575,000,000					14,575,000,000
Business Acquisition, Impact Of Merger [Abstract]
Revenues	4,255,000,000			4,031,000,000		11,858,000,000		10,539,000,000
Net income	485,000,000			87,000,000		795,000,000		419,000,000
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	3,000,000			4,000,000		6,000,000		68,000,000
Non-Merger Severance Costs								34,000,000
Stock Compensation Expense				2,000,000				4,000,000
Other Expense Charges								4,000,000
Total Severance Benefits				6,000,000	[3]			76,000,000	[3]
Payments						20,000,000
Restructuring Reserve, Intercompany Allocation	2,000,000			0		3,000,000		40,000,000
Restructuring Reserve, Period End	14,000,000					14,000,000
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Reserve [Roll Forward]
Severance Charges						1,000,000	[4]
Exelon Generation Co L L C [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Severance Charges	11,000,000			3,000,000		12,000,000		8,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Group Acquisition [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	32,000,000			79,000,000		75,000,000		283,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net Abstract
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment	4,054,000,000					4,054,000,000
Current Assets	3,638,000,000					3,638,000,000
Unamortized Energy Contracts	3,218,000,000					3,218,000,000
Other intangibles, trade name and retail relationships	457,000,000					457,000,000
Investment in affiliates	1,942,000,000					1,942,000,000
Other assets	1,266,000,000					1,266,000,000
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract
Current liabilities	2,804,000,000					2,804,000,000
Unamortized energy contracts	1,512,000,000					1,512,000,000
Long-term debt, including current maturities	2,972,000,000					2,972,000,000
Business Combination Aquisition Of Less than 100 Percent Noncontrolling Interest Fair Value	90,000,000					90,000,000
Deferred credits and other liabilities and preferred securities	1,933,000,000					1,933,000,000
Total liabilities,preferred securities and noncontrolling Interest	9,311,000,000					9,311,000,000
Total purchase price	5,264,000,000					5,264,000,000
Business Acquisition, Pro Forma Information [Abstract]
Business Acquisition, Pro Forma Revenue				4,293,000,000				12,753,000,000
Business Acquisition, Pro Forma Net Income (Loss)				282,000,000				805,000,000
Exelon Generation Co L L C [Member] | Perryman Construction [Member]
Business Acquisition, Regulatory Matters [Abstract]
Business Acquisition, Construction Cost	80,000,000					80,000,000
Business Acquisition, Divesture Wattage						120
Commonwealth Edison Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	1,156,000,000			1,484,000,000		3,395,000,000		4,154,000,000
Net income	126,000,000			90,000,000		140,000,000		219,000,000
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start			1,000,000			1,000,000
Severance Charges				1,000,000	[5]			16,000,000	[5]
Stock Compensation Expense				1,000,000	[5]			1,000,000	[5]
Other Expense Charges								1,000,000	[5]
Total Severance Benefits				2,000,000	[3],[5]			18,000,000	[3],[5]
Restructuring Reserve, Intercompany Allocation				2,000,000				16,000,000
Restructuring Reserve, Period End	1,000,000					1,000,000
Merger related severance regulatory asset				2,000,000				18,000,000
Commonwealth Edison Co [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Severance Charges	1,000,000			1,000,000		2,000,000		1,000,000
Commonwealth Edison Co [Member] | Constellation Energy Group Acquisition [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	5,000,000			8,000,000		14,000,000		34,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						10,000,000		30,000,000
PECO Energy Co [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	728,000,000			806,000,000		2,295,000,000		2,396,000,000
Net income	92,000,000			123,000,000		292,000,000		300,000,000
Restructuring Reserve [Roll Forward]
Severance Charges				1,000,000				8,000,000
Non-Merger Severance Costs								1,000,000
Total Severance Benefits				1,000,000	[3]			8,000,000	[3]
Restructuring Reserve, Intercompany Allocation				1,000,000				8,000,000
PECO Energy Co [Member] | Constellation Energy Group Acquisition [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	3,000,000			3,000,000		8,000,000		13,000,000
Baltimore Gas and Electric Company [Member]
Business Acquisition, Impact Of Merger [Abstract]
Revenues	737,000,000			720,000,000		2,271,000,000		2,032,000,000
Revenues Impact				720,000,000				1,388,000,000
Net Income Loss Impact				0				(49,000,000)
Net income	53,000,000			0		160,000,000		(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				1,000,000	[6]			18,000,000	[6]
Other Expense Charges								1,000,000	[6]
Total Severance Benefits				1,000,000	[3],[6]			19,000,000	[3],[6]
Payments						4,000,000
Restructuring Reserve, Intercompany Allocation				1,000,000				7,000,000
Restructuring Reserve, Period End	7,000,000					7,000,000
Merger related severance regulatory asset				1,000,000				19,000,000
Baltimore Gas and Electric Company [Member] | Other Severance Charges [Member]
Restructuring Reserve [Roll Forward]
Severance Charges				1,000,000				2,000,000
Baltimore Gas and Electric Company [Member] | Constellation Energy Group Acquisition [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	2,000,000			1,000,000		5,000,000		172,000,000
Business Acquisition, Impact Of Merger [Abstract]
Regulatory Assets Transfer Changes						5,000,000		19,000,000
Constellation Energy Group Acquisition [Member] | Total Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired						586,000,000
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	(1,370,000,000)					(1,370,000,000)
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	90,000,000					90,000,000
Future amortization expense in year two	118,000,000					118,000,000
Future amortizationExpense in year three	60,000,000					60,000,000
Future amortization expense in year four	11,000,000					11,000,000
Future amortization expense in year five	21,000,000					21,000,000
Future amortization expense in year six and thereafter						286,000,000
Customer Relationships [Member]
Finite Lived Intangible Assets Net [Abstract]
Amortization Of Contracts	8,000,000			2,000,000		17,000,000		9,000,000
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]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired						183,000,000
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	214,000,000					214,000,000
Finite lived intangible assets accumulated amortization	(31,000,000)					(31,000,000)
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	5,000,000					5,000,000
Future amortization expense in year two	19,000,000					19,000,000
Future amortizationExpense in year three	18,000,000					18,000,000
Future amortization expense in year four	18,000,000					18,000,000
Future amortization expense in year five	18,000,000					18,000,000
Future amortization expense in year six and thereafter						105,000,000
Trade Names [Member]
Finite Lived Intangible Assets Net [Abstract]
Amortization Of Contracts	8,000,000			6,000,000		20,000,000		14,000,000
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]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired						203,000,000
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	243,000,000					243,000,000
Finite lived intangible assets accumulated amortization	(40,000,000)					(40,000,000)
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	6,000,000					6,000,000
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						101,000,000
Power Supply Contracts [Member]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets net	32,000,000					32,000,000
Amortization Of Contracts	40,000,000			261,000,000		372,000,000		794,000,000
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]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired						200,000,000
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	1,499,000,000	[7]				1,499,000,000	[7]
Finite lived intangible assets accumulated amortization	(1,299,000,000)	[7]				(1,299,000,000)	[7]
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future amortization expense within the next twelve months	79,000,000	[7]				79,000,000	[7]
Future amortization expense in year two	75,000,000	[7]				75,000,000	[7]
Future amortizationExpense in year three	18,000,000	[7]				18,000,000	[7]
Future amortization expense in year four	(31,000,000)	[7]				(31,000,000)	[7]
Future amortization expense in year five	(21,000,000)	[7]				(21,000,000)	[7]
Future amortization expense in year six and thereafter						$ 80,000,000	[7]

[1] For the three months ended September 30, 2013 and 2012, utility taxes of $21 million and $28 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2013 and 2012, utility taxes of $65 million and $67 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2013 and 2012, utility taxes of $33 million and $40 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2013 and 2012, utility taxes of $20 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2013 and 2012, utility taxes of $60 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2013 and 2012, utility taxes of $182 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2013 and 2012, utility taxes of $97 million and $108 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2013 and period of March 12, 2012 through September 30, 2012, utility taxes of $62 million and $42 million, respectively, are included in revenues and expenses for BGE.

[3] 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.

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

[5] ComEd established regulatory assets of $2 million and $18 million for severance benefits costs for the three and nine months ended September 30, 2012, respectively. The majority of these costs are expected to be recovered over a five-year period.

[6] BGE established regulatory assets of $1 million and $19 million for severance benefits costs for the three and nine months ended September 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.

[7] Includes the fair value of BGE's power and gas supply contracts of $32 million for which an offsetting regulatory asset was also recorded