Regulatory Matters - Narrative (Details) $ in Millions														1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	17 Months Ended
		Oct. 20, 2015 USD ($)	Oct. 19, 2015 USD ($)	Sep. 10, 2015 USD ($)	May. 27, 2015 USD ($)	May. 19, 2015 USD ($)	Apr. 24, 2015 USD ($)	Apr. 15, 2015 USD ($)	Mar. 27, 2015 USD ($)	Dec. 08, 2014	Aug. 21, 2014 USD ($)	Dec. 13, 2013 USD ($)	Feb. 27, 2013	Aug. 31, 2010 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Jun. 11, 2014	Jun. 03, 2014 USD ($)	Apr. 28, 2014	Aug. 23, 2013 USD ($)	May. 17, 2013 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															$ 6,779.0		$ 6,779.0		$ 6,923.0	$ 6,779.0
Rate of Return on Common Equity, Incentive Basis Points															0.50%		0.50%			0.50%
Regulatory assets															$ 6,000.0		$ 6,000.0		6,076.0	$ 6,000.0
Transmission Rate Formula, First Basis Points Credited																	0.50%
Business Combination, Integration Related Costs															21.0	$ 32.0	$ 47.0	$ 57.0		110.0
Regulatory Liabilities															4,545.0		4,545.0		4,860.0	4,545.0
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															1,145.0		$ 1,145.0		1,201.0	1,145.0
Public Utilities, Requested Rate Increase (Decrease), Amount								$ 50.0
Expected revenue adjustment for current year								$ 92.0
Expected revenue adjustment for prior year																			$ 142.0
Requested Debt and Equity Return on Distribution								7.05%
Requested ROE								9.14%											9.09%
Weighted Average Debt And Equity Return Electric Distribution																			7.02%
Weighted Average Debt And Equity Return								8.61%											8.62%
Gross transmission revenue requirement						$ 68.0
Transmission revenue true up								$ 18.0
Net transmission revenue requirement						$ 86.0
Estimated number of smart meters to be installed																					4,000,000
Smart Meters Installed																	1,600,000
Regulatory assets															913.0		$ 913.0		$ 852.0	913.0
Rate Of Return On Common Equity								11.50%
Business Combination, Integration Related Costs															3.0	1.0	10.0	1.0
Regulatory Liabilities															3,585.0		3,585.0		3,780.0	3,585.0
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															1,589.0		1,589.0		1,558.0	1,589.0
Spend on smart grid investments															155.0		$ 155.0			155.0
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 127.0					$ 190.0
Public Utilities, Requested Rate Increase (Decrease), Percentage									10.95%
TotalSmartMetersInstalled																	1,700,000
SmartMeterFundingSGIG																	$ 200.0
Smart meter spend to date															579.0		579.0			579.0
Smart grid infrastructure spend to date															155.0		155.0			155.0
Total smart grid and smart meter investment grant amount															591.0		591.0			591.0
Regulatory assets															1,557.0		1,557.0		1,529.0	1,557.0
Amount of Regulatory Costs Not yet Approved															534.0		534.0			534.0
Business Combination, Integration Related Costs															2.0	1.0	4.0	1.0
Regulatory Liabilities															640.0		640.0		747.0	640.0
Total Projected Natural Gas LTIIP Spend					$ 275.0
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															742.0		742.0		724.0	742.0
Weighted Average Debt And Equity Return							8.46%																8.53%
Adjustment to Requested increase in electric revenues																								$ 83.0
Requested increase in gas revenues																									$ 24.0
Rate of return on common equity electric distribution												9.75%
Rate of return on common equity gas distribution												9.60%
Increase in electric delivery service revenue resulting from rate case settlement or order.												$ 34.0
Increase in gas delivery service revenue resulting from rate case settlement or order.												$ 12.0
Gross transmission revenue requirement							$ 13.0
Transmission revenue true up							3.0
Net transmission revenue requirement							$ 10.0
Estimated number of smart meters to be installed														2,000,000
Reimbursements received from the DOE														$ 200.0
Regulatory assets															485.0		485.0		510.0	485.0
Total Projected smart meter smart grid spend														$ 480.0
Rate Of Return On Common Equity							11.30%
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint										8.80%			8.70%
Business Combination, Integration Related Costs															2.0	1.0	5.0	1.0
Regulatory Liabilities															255.0		255.0		244.0	255.0
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs																	43.0
Other Commitment															3.5		3.5			3.5
Business Combination, Integration Related Costs															9.0	$ 3.0	24.0	$ 4.0
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Minimum Purchase Obligation																						$ 25.0
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Maximum Purchase Obligation																						$ 35.0
Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															240.0		240.0		371.0	240.0
Under Recovered Distribution Service Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[1]														240.0		240.0		371.0	240.0
CostRecoveryForSignificantOneTimeEvents																	56.0		85.0
UnderOverRecoveredDistributionServiceCosts																	184.0		286.0
Business Combination, Integration Related Costs																	13.0		19.0
RegulatoryAssetsDueToDeferredStormCosts																	43.0		66.0
Under Recovered Distribution Service Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0.0		0.0		0.0	0.0
Under Recovered Distribution Service Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0.0		0.0		0.0	0.0
AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															373.0		373.0		296.0	373.0
AMI Expenses [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															130.0		130.0		91.0	130.0
AMI Expenses [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															64.0		64.0		77.0	64.0
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															179.0		179.0		128.0	179.0
Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															271.0		271.0		248.0	271.0
Energy Efficiency And Demand Response Programs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0.0		0.0		0.0	0.0
Energy Efficiency And Demand Response Programs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0.0		0.0		0.0	0.0
Energy Efficiency And Demand Response Programs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															271.0		271.0		248.0	271.0
Transmission Rate Formula [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory asset															26.0		26.0		21.0	26.0
Net Regulatory Asset															26.0		26.0		21.0	26.0
Transmission Rate Formula [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory asset															5.0		5.0		1.0	5.0
Net Regulatory Asset															5.0		5.0		1.0	5.0
Distribution formula Rate [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net Regulatory Assets															240.0		240.0		371.0	240.0
Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															67.0		67.0		48.0	67.0
Under Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[2]														33.0		33.0		33.0	33.0
ElectricTransmissionCostsUnderRecovery																	26.0		22.0
Business Combination, Integration Related Costs																	7.0		7.0
Under Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0.0		0.0		0.0	0.0
Under Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[3]														34.0		$ 34.0		15.0	34.0
Business Combination, Integration Related Costs																			4.0
FERC Transmission Complaint [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Approved ROE													10.80%
Revenue Reduction											$ 14.0
Customer Refund Liability, Noncurrent											13.0
Customer Refund											13.0
Cash Collected											$ 27.0
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 68.0
Expected revenue adjustment for current year			8.0
Expected revenue adjustment for prior year			10.0
Revenue Reduction			$ 18.0
Scenario, Forecast [Member] | FERC Transmission Complaint [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue Reduction		$ (11.0)
Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities															134.0		$ 134.0		84.0	134.0
Over Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	[2]														46.0		46.0		19.0	46.0
Over Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	[4]														70.0		70.0		58.0	70.0
Over Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	[3]														$ 18.0		$ 18.0		$ 7.0	$ 18.0

[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] 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.

[4] (e)As of September 30, 2015, PECO's regulatory liability of $70 million included $33 million related to the DSP program, $31 million related to the over-recovered natural gas costs under the PGC and $6 million related to over-recovered electric transmission costs. As of December 31, 2014, PECO's regulatory liability of $58 million included $39 million related to the DSP program, $16 million related to the over-recovered natural gas costs under the PGC and $3 million related to the over-recovered electric transmission costs.