Regulatory Matters - Narrative (Details) MWh in Millions, $ in Millions																									1 Months Ended		3 Months Ended						9 Months Ended			12 Months Ended		156 Months Ended
		Dec. 31, 2030	Oct. 27, 2017 USD ($)	Oct. 20, 2017 USD ($)	Sep. 28, 2017 USD ($)	Sep. 11, 2017 USD ($)	Sep. 08, 2017 USD ($)	Aug. 17, 2017 USD ($)	Jul. 25, 2017 USD ($)	Jul. 14, 2017 USD ($)	Jun. 14, 2017 USD ($)	Jun. 09, 2017 USD ($)	Apr. 06, 2017 USD ($)	Mar. 30, 2017 USD ($)	Mar. 24, 2017 USD ($)	Mar. 22, 2017 USD ($)	Mar. 08, 2017 USD ($)	Feb. 15, 2017 USD ($)	Feb. 01, 2017 USD ($)	Dec. 17, 2016 USD ($)	Dec. 06, 2016 USD ($)	Jul. 16, 2016 USD ($)	May 17, 2016 USD ($)	Oct. 22, 2015 USD ($)	Jun. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) Monetary_per_Decimal MWh		Sep. 30, 2016 USD ($)	Dec. 31, 2017	Dec. 31, 2016 USD ($)	Dec. 31, 2030 USD ($)	Jun. 01, 2019	Jun. 01, 2018	Aug. 01, 2017 USD ($)	Jul. 21, 2017 USD ($)	Jun. 01, 2017	Aug. 31, 2010 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											$ 5,102.0						$ 5,102.0				$ 4,789.0
Regulatory Assets																											11,502.0						11,502.0				11,388.0
Regulatory Liability, Current																											553.0						553.0				602.0
Regulatory Liability, Noncurrent																											4,549.0						4,549.0				4,187.0
Other Commitment																											2,879.0						2,879.0
Revenues																											8,769.0			$ 9,002.0			25,149.0		$ 23,486.0
Fair Value, Net Asset (Liability)																											2,400.0						2,400.0
AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											660.0						660.0				701.0
Zero Emission Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											71.0						71.0
Renewable Portfolio Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											46.0						46.0
Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											62.0						62.0				185.0
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																																										$ 235.0
Customer Refund Liability, Noncurrent																													$ 20.0
Other Commitment																											2,272.0						2,272.0
Revenues																									$ 12.0		4,751.0			5,035.0			13,812.0		13,363.0
License Costs																																	30.0
Exelon Generation Co L L C [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																										$ 101.0
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											3.0						3.0
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											7.0						7.0
Exelon Generation Co L L C [Member] | Zero Emission Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																											118.0						191.0
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]																																11.0
Public Utilities, Requested Increase (Decrease), Amount												$ 7.0																					$ 44.0	[1]
Public Utilities, Approved Rate Increase (Decrease), Amount						$ 12.0
Public Utilities, Approved Return on Equity, Percentage						8.40%																											11.50%	[1],[2]
Public Utilities, Approved Equity Capital Structure, Percentage						6.47%																											8.43%	[1],[3]
SocialCarbonCost | Monetary_per_Decimal																																	16.5
Purchase Obligation																																										$ 170.0
Regulatory Liabilities																											3,984.0						$ 3,984.0				3,698.0
DecouplingImpactOnOperatingRevenuesAndRegulatoryAssets																																	21.0
LowIncomeEnergyAssistanceContributionAnnual																																	$ 10.0
LowIncomeEnergyAssistanceContributionLength																																	5
Low Income Sector Consumption Reduction Targets Act 129 Phase II																																	0.10%
CumulativeAnnualEnergyEfficiencyGoal | MWh																																	88
Regulatory Assets																											1,574.0						$ 1,574.0				1,167.0
Regulatory Liability, Current																											249.0						249.0				329.0
Regulatory Liability, Noncurrent																											3,735.0						$ 3,735.0				$ 3,369.0
Renewable Energy Resources Cumulatively Increase																																	1.50%
RenewableEnergyRetailLoad																																											50.00%
Other Commitment																											234.0						$ 234.0
Revenues																											1,571.0			1,497.0			4,227.0		4,031.0
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																																	96.0
Public Utilities, Requested Increase (Decrease), Amount																																	78.0
Public Utilities, Approved Rate Increase (Decrease), Amount																$ 18.0					$ 127.0												$ 18.0
Public Utilities, Requested Equity Capital Structure, Percentage																																	6.47%
Public Utilities, Requested Rate Increase (Decrease), Percentage																																	8.40%
Public Utilities, Approved Equity Capital Structure, Percentage																																					6.45%
Public Utilities, Approved Rate Increase (Decrease), Percentage																																					8.34%
Commonwealth Edison Co [Member] | Electric Distribution [Member] | 2016 Requirement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																					134.0
Commonwealth Edison Co [Member] | Electric Distribution [Member] | 2015 Requirement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																					$ 7.0
Commonwealth Edison Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Renewable Energy Resources Cumulatively Increase																																	11.50%
Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
ResidentialCustomerRateIncrease | Monetary_per_Decimal																																	0.25
CommercialAndIndustrialCustomerRateIncrease																																	1.30%
Renewable Energy Resources Cumulatively Increase																																	25.00%
Commonwealth Edison Co [Member] | Deferred EE Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											83.0						$ 83.0
Commonwealth Edison Co [Member] | Energy Efficiency Program [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											78.0						78.0
Commonwealth Edison Co [Member] | Renewable Portfolio Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											7.0						7.0
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											159.0						159.0				$ 164.0
Commonwealth Edison Co [Member] | Zero Emission Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											71.0						71.0
Commonwealth Edison Co [Member] | Renewable Portfolio Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											46.0						46.0
Restricted Cash																											45.0						45.0
Regulatory Liability, Current																											10.0						10.0
Regulatory Liability, Noncurrent																											20.0						20.0
Commonwealth Edison Co [Member] | ACPpayment member [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											38.0						38.0
Commonwealth Edison Co [Member] | Over recovered EE Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											(5.0)						(5.0)
Commonwealth Edison Co [Member] | EDArefund Member [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											80.0						80.0
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											33.0						33.0				0.0
Commonwealth Edison Co [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
EnergyEfficiencyAnnualCumulativeSavings		21.50%																																		6.60%
RenewableEnergyRetailLoad																																							100.00%	75.00%
Commonwealth Edison Co [Member] | Subsequent Event [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
FutureEnergyEfficiencySpending																																						$ 250.0
Commonwealth Edison Co [Member] | Subsequent Event [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
FutureEnergyEfficiencySpending																																						$ 400.0
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																												$ 22.0
Public Utilities, Requested Equity Capital Structure, Percentage																												11.00%
Regulatory Liabilities																											719.0						719.0				644.0
Regulatory Assets																											1,809.0						1,809.0				1,710.0
Regulatory Liability, Current																											159.0						159.0				127.0
Regulatory Liability, Noncurrent																											560.0						560.0				517.0
Total Projected Natural Gas LTIIP Spend											$ 762.0													$ 275.0
Other Commitment																											240.0						240.0
Revenues																											715.0			788.0			2,141.0		2,293.0
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											40.0						40.0				49.0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											29.0						29.0				41.0
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]																																26.0
Public Utilities, Requested Increase (Decrease), Amount	[1]																																$ 31.0
Public Utilities, Approved Return on Equity, Percentage	[1],[2]																																10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[3]																																7.47%
Regulatory Liabilities																											147.0						$ 147.0				160.0
Regulatory Assets																											705.0						705.0				712.0
Regulatory Liability, Current																											63.0						63.0				50.0
Regulatory Liability, Noncurrent																											84.0						84.0				110.0
Estimated number of smart meters to be installed																																												2,000,000
Total smart grid and smart meter investment grant amount																																												$ 480.0
Reimbursements received from the DOE																																												$ 200.0
Other Commitment																											13.0						13.0
Proposed Capital Expenditure	[1],[4]																																8.0
Revenues																											738.0			812.0			2,363.0		2,421.0
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											219.0						219.0				230.0
Amount of Impairment to Carrying Amount of Regulatory Assets																															$ 52.0
Baltimore Gas and Electric Company [Member] | Unamortized AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											133.0						133.0
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											54.0				56.0		54.0
Baltimore Gas and Electric Company [Member] | Recoverable Smart Meter Related Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											32.0						32.0
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											0.0						0.0				0.0
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]																																20.0
Public Utilities, Requested Increase (Decrease), Amount	[1]																																$ 5.0
Public Utilities, Approved Return on Equity, Percentage	[1],[2]																																10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[3]																																7.92%
Regulatory Liabilities																											26.0						$ 26.0				31.0
Regulatory Assets																											880.0						880.0				852.0
Regulatory Liability, Current																											5.0						5.0				11.0
Regulatory Liability, Noncurrent																											21.0						21.0				20.0
Projected Capital Expenditures																											500.0
Other Commitment																											20.0						20.0
Alternative Net Capital Requirement																											250.0						250.0
Capital ProjectFundedByBonds																											187.5
CapitalProjectFundedByAgency																											62.5
Revenues																											604.0			$ 635.0			1,649.0		1,695.0
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																			$ 77.0								67.0
Public Utilities, Requested Increase (Decrease), Amount															$ 69.0																$ 86.0
Public Utilities, Approved Rate Increase (Decrease), Amount									$ 37.0
Public Utilities, Requested Rate Increase (Decrease), Percentage															10.10%															10.60%
Public Utilities, Approved Rate Increase (Decrease), Percentage									9.50%
TaxAdjustmentIncludedInPublicUtilitiesRequestedRateIncreaseDecreaseAmount															$ 18.0
Potomac Electric Power Company [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											163.0						163.0				174.0
Potomac Electric Power Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											0.0						0.0				3.0
Potomac Electric Power Company [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 32.0	$ 34.0
Public Utilities, Approved Rate Increase (Decrease), Percentage				0.00%
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																											26.0						26.0
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Minimum [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																											6.0						6.0
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Maximum [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																											7.0						7.0
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]																																14.0
Public Utilities, Requested Increase (Decrease), Amount	[1]																																$ 6.0
Public Utilities, Requested Return on Equity, Percentage								10.10%		10.10%													10.60%
Public Utilities, Approved Return on Equity, Percentage	[1],[2]																																10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[3]																																7.16%
Regulatory Liabilities																											128.0						$ 128.0				140.0
Regulatory Assets																											369.0						369.0				348.0
Regulatory Liability, Current																											42.0						42.0				43.0
Regulatory Liability, Noncurrent																											86.0						86.0				97.0
Public Utilities, Interim Rate Increase (Decrease), Amount								$ 2.5														$ 2.5
Customer Refund Liability, Noncurrent																																									$ 5.0
Other Commitment																											11.0						11.0
Revenues																											327.0			$ 331.0			971.0		974.0
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Increase (Decrease), Amount								13.0															$ 22.0
Public Utilities, Approved Rate Increase (Decrease), Amount													$ 4.9							$ 10.0
Public Utilities, Approved Rate Increase (Decrease), Percentage													9.70%
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					$ 22.0			31.0																								$ 32.0
Public Utilities, Requested Increase (Decrease), Amount								$ 24.0		$ 27.0							$ 60.0						$ 63.0
Public Utilities, Approved Rate Increase (Decrease), Amount																		$ 38.0		$ 30.0									$ 31.5
Public Utilities, Approved Return on Equity, Percentage																		9.60%
Public Utilities, Approved Rate Increase (Decrease), Percentage																													9.70%
Projected Capital Expenditures																		$ 5.0
Delmarva Power and Light Company [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											79.0						79.0				84.0
Delmarva Power and Light Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											0.0						0.0				0.0
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]																																42.0
Public Utilities, Requested Increase (Decrease), Amount	[1]																																$ 20.0
Public Utilities, Approved Return on Equity, Percentage	[1],[2]																																10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[3]																																8.02%
Regulatory Liabilities																											18.0						$ 18.0				25.0
Regulatory Assets																											504.0						504.0				501.0
Regulatory Liability, Current																											18.0						18.0				25.0
Regulatory Liability, Noncurrent																											0.0						0.0				0.0
Projected Capital Expenditures																											79.0
Other Commitment																											9.0						9.0
Proposed Capital Expenditure																			$ 29.0									$ 32.0
Revenues																											370.0			$ 421.0			915.0		$ 982.0
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Increase (Decrease), Amount							$ 43.0			$ 73.0				$ 70.0
Public Utilities, Requested Rate Increase (Decrease), Percentage							9.60%							10.10%
Atlantic City Electric Company [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																											0.0						0.0				0.0
Atlantic City Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											$ 0.0						$ 0.0				$ 0.0

[1] All rates are effective June 2017, subject to review by the FERC and other parties, which is due by fourth quarter 2017.

[2] As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50 basis point incentive adder for being a member of a regional transmission organization.

[3] Represents the weighted average debt and equity return on transmission rate bases.

[4] BGE's transmission revenues include a FERC approved dedicated facilities charge to recover the costs of providing transmission service to specifically designated load by BGE.