Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended			12 Months Ended	17 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014	Dec. 31, 2014	Sep. 30, 2015
Regulatory Assets [Line Items]
Current		$ 779			$ 779			$ 847	$ 779
Noncurrent		6,000			6,000			6,076	6,000
Regulatory Assets		6,779			6,779			6,923	6,779
Business Combination, Integration Related Costs		21		$ 32	47		$ 57		110
Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3,138			3,138			3,256	3,138
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,589			1,589			1,542	1,589
AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		373			373			296	373
Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		240			240			371	240
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		50			50			57	50
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		170			170			190	170
Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10			10			12	10
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		106			106			116	106
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		289			289			257	289
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		54			54			67	54
Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		243			243			207	243
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		67			67			48	67
Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2			2			3	2
Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		23			23			30	23
Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		101			101			160	101
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		271			271			248	271
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6			6			8	6
ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1			1			2	1
Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		39			39			46	39
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7			7			7	7
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Current		232			232			349	232
Noncurrent		913			913			852	913
Regulatory Assets		1,145			1,145			1,201	1,145
Business Combination, Integration Related Costs		3		1	10		1
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		66			66			64	66
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		130			130			91	130
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	240			240			371	240
UnderOverRecoveredDistributionServiceCosts					184			286
CostRecoveryForSignificantOneTimeEvents					56			85
RegulatoryAssetsDueToDeferredStormCosts					43			66
Business Combination, Integration Related Costs					13			19
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		48			48			53	48
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		66			66			74	66
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		256			256			219	256
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		54			54			67	54
Commonwealth Edison Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		243			243			207	243
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	33			33			33	33
Business Combination, Integration Related Costs					7			7
ElectricTransmissionCostsUnderRecovery					26			22
Underrecovered Electric Supply cost								4
Commonwealth Edison Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Commonwealth Edison Co [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9			9			22	9
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Current		32			32			29	32
Noncurrent		1,557			1,557			1,529	1,557
Regulatory Assets		1,589			1,589			1,558	1,589
Business Combination, Integration Related Costs		2		1	4		1
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,446			1,446			1,400	1,446
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		64			64			77	64
PECO Energy Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2			2			4	2
PECO Energy Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		22			22			26	22
PECO Energy Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		32			32			37	32
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
PECO Energy Co [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		23			23			14	23
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Current		257			257			214	257
Noncurrent		485			485			510	485
Regulatory Assets		742			742			724	742
Business Combination, Integration Related Costs		2		$ 1	5		$ 1
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		77			77			78	77
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		179			179			128	179
Baltimore Gas and Electric Company [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8			8			9	8
Baltimore Gas and Electric Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10			10			12	10
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		18			18			16	18
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	[3]		1	[3]		1	1	[3]
Baltimore Gas and Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0			0			0	0
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4]	34			$ 34			15	34
Business Combination, Integration Related Costs								4
Underrecovered Electric Supply cost					$ 29			10
Environmental Restoration Costs					5			1
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2	[3]		2	[3]		3	2	[3]
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		23	[3]		23	[3]		30	23	[3]
Baltimore Gas and Electric Company [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		101			101			160	101
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		271			271			248	271
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6			6			8	6
Baltimore Gas and Electric Company [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1			1			2	1
Baltimore Gas and Electric Company [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4			4			7	4
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[5]	$ 7			7			7	$ 7
UnderRecoveredElectricRevenueDecoupling								$ 7
Over Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Underrecovered Electric Supply cost					$ 4

[1] As of September 30, 2015, ComEd’s regulatory asset of $240 million was comprised of $184 million for the applicable annual reconciliations and $56 million related to significant one-time events including $43 million of deferred storm costs and $13 million of Constellation merger and integration related costs. As of December 31, 2014, ComEd’s regulatory asset of $371 million was comprised of $286 million for the applicable annual reconciliations and $85 million related to significant one-time events, including $66 million of deferred storm costs and $19 million of Constellation merger and integration related costs. See Note 4 — Mergers, Acquisitions, and Dispositions of the Exelon 2014 Form 10-K for further information.

[2] As of September 30, 2015, ComEd’s regulatory asset of $33 million included $26 million associated with transmission costs recoverable through its FERC approved formulate rate, and $7 million of Constellation merger and integration costs to be recovered upon FERC approval. As of September 30, 2015, ComEd’s regulatory liability of $46 million included $24 million related to over-recovered energy costs for hourly customers and $22 million associated with revenues received for renewable energy requirements. As of December 31, 2014, ComEd’s regulatory asset of $33 million included $4 million related to under-recovered energy costs for non-hourly customers, $22 million associated with transmission costs recoverable through its FERC approved formulate rate, and $7 million of Constellation merger and integration costs to be recovered upon FERC approval. As of December 31, 2014, ComEd’s regulatory liability of $19 million included $3 million related to over-recovered energy costs for hourly customers and $16 million associated with revenues received for renewable energy requirements.

[3] (g)In accordance with the MDPSC approved 2014 electric and natural gas distribution rate case orders, the recovery periods for these regulatory assets were revised, effective in January 2015.

[4] As of September 30, 2015, BGE's regulatory asset of $34 million included $5 million associated with transmission costs recoverable through its FERC approved formula rate and $29 million related to under-recovered electric energy costs. As of September 30, 2015, BGE's regulatory liability of $18 million related to $9 million of over-recovered natural gas supply costs and $14 million of over-recovered energy costs, offset by $4 million of Constellation merger and integration costs and $1 million of abandonment costs to be recovered upon FERC approval. As of December 31, 2014, BGE's regulatory asset of $15 million included $10 million related to under-recovered electric energy costs, $4 million of Constellation merger and integration costs and $1 million of abandonment costs to be recovered upon FERC approval. As of December 31, 2014, BGE's regulatory liability of $7 million related to over-recovered natural gas supply costs.

[5] (f)Represents the electric and gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2015, BGE had a regulatory asset of $7 million related to under-recovered electric revenue decoupling and a regulatory liability of $27 million related to over-recovered natural gas revenue decoupling. As of December 31, 2014, BGE had a regulatory asset of $7 million related to under-recovered electric revenue decoupling and a regulatory liability of $12 million related to over-recovered natural gas revenue decoupling.