Regulatory Matters - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended	0 Months Ended					1 Months Ended	0 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014	Dec. 08, 2014	Aug. 21, 2014	Dec. 13, 2013	May 17, 2013	Feb. 27, 2013	Aug. 31, 2010	Oct. 20, 2015	Apr. 28, 2014	Aug. 23, 2013	Jun. 03, 2014
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	$ 6,872				$ 6,923
Rate of Return on Common Equity, Incentive Basis Points	0.50%
Regulatory assets	6,068				6,076
Transmission Rate Formula, First Basis Points Credited	0.50%
Business Combination, Integration Related Costs	69
Regulatory Liabilities	4,987				4,860
Revenues	8,830	[1]	7,237	[1]
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	1,183				1,201
Public Utilities, Requested Rate Increase (Decrease), Amount	50
Expected revenue adjustment for current year	92
Expected revenue adjustment for prior year					142
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	73
Transmission revenue true up	18
Net transmission revenue requirement	91
Regulatory assets	866				852
Rate Of Return On Common Equity	11.50%
Common Equity Component Cap	55.00%
Regulatory Liabilities	3,823				3,780
Revenues	1,185		1,134
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
CostRecoveryForSignificantOneTimeEvents	76				85
UnderOverRecoveredDistributionServiceCosts	240				286
Business Combination, Integration Related Costs	17				19
RegulatoryAssetsDueToDeferredStormCosts	59				66
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	1,584				1,558
Spend on smart grid investments	155
Public Utilities, Requested Rate Increase (Decrease), Amount	190
Requested ROE	10.95%
Public Utilities, Requested Rate Increase (Decrease), Percentage	4.40%
TotalSmartMetersInstalled	1,700,000
SmartMeterFundingSGIG	200
Smart meter spend to date	568
Smart grid infrastructure spend to date	155
Total smart grid and smart meter investment grant amount	591
Regulatory assets	1,543				1,529
Amount of Regulatory Costs Not yet Approved	275
Regulatory Liabilities	781				747
Revenues	985		993
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	678				724
Public Utilities, Requested Rate Increase (Decrease), Amount									24
Weighted Average Debt And Equity Return	8.46%												8.53%
Adjustment to Requested increase in electric revenues														83
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
Increase in gas delivery service revenue resulting from rate case settlement or order.								12
Gross transmission revenue requirement	13
Transmission revenue true up	3
Net transmission revenue requirement	10
Revenue Reduction							14
Customer Refund Liability, Noncurrent							13
Estimated number of smart meters to be installed											2,000,000
Reimbursements received from the DOE											200
Regulatory assets	491				510
Total Projected smart meter smart grid spend											480
Customer Refund							13
Rate Of Return On Common Equity	11.30%
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint						8.80%				8.70%
Regulatory Liabilities	311				244
Revenues	1,036		1,054
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs	40
Other Commitment	3.5
Revenues	5,840		4,390
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Minimum Purchase Obligation															25
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Maximum Purchase Obligation															35
Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	316				371
Under Recovered Distribution Service Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	316				371
Under Recovered Distribution Service Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	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
AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	325				296
AMI Expenses [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	106				91
AMI Expenses [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	76				77
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	143				128
Regulatory assets	143				128
Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	230				248
Energy Efficiency And Demand Response Programs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	0				0
Energy Efficiency And Demand Response Programs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	0				0
Energy Efficiency And Demand Response Programs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	230				248
Transmission Rate Formula [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory asset	25				21
Net Regulatory Asset	25				21
Transmission Rate Formula [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory asset	2				1
Net Regulatory Asset	2				1
Distribution formula Rate [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net Regulatory Assets	316				371
Stride Program [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets	1
Under-Recovered Electric Supply Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
ElectricTransmissionCostsUnderRecovery	5				4
Business Combination, Integration Related Costs	7				7
Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	41				48
Under Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	37				33
ElectricTransmissionCostsUnderRecovery	25				22
Under Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	0				0
Under Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	4				15
Renewable Energy Requirement [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues	18		16
FERC Transmission Complaint [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Approved ROE										10.80%
Scenario, Forecast [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue Reduction												(11)
Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	142				84
Over Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
ElectricTransmissionCostsUnderRecovery	5				3
Regulatory Liabilities	23				19
Over Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	84				58
Over Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities	$ 35				$ 7

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