Regulatory Matters - Narrative (Details) - USD ($) $ in Millions																						3 Months Ended		12 Months Ended	48 Months Ended
	Apr. 20, 2018	Apr. 17, 2018	Mar. 29, 2018	Mar. 26, 2018	Mar. 17, 2018	Mar. 08, 2018	Mar. 02, 2018	Feb. 09, 2018	Feb. 06, 2018	Feb. 05, 2018	Jan. 31, 2018	Jan. 18, 2018	Jan. 02, 2018	Dec. 19, 2017	Dec. 18, 2017	Nov. 16, 2017	Nov. 07, 2017	Oct. 18, 2017	Aug. 17, 2017	Jul. 14, 2017	May 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2022	Dec. 31, 2017	Apr. 21, 2016
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						$ 9,308.0				$ 9,288.0
Regulatory Liabilities																						10,246.0				10,388.0
Revenues																						9,693.0	$ 8,747.0
Payments to Acquire Property, Plant, and Equipment																						1,880.0	2,009.0
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						82.0
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																						5,512.0	4,878.0
Payments to Acquire Property, Plant, and Equipment																						628.0	625.0
License Costs																						32.0
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											$ 3.0
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											$ 7.0
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						1,351.0				1,279.0
Regulatory Liabilities																						6,424.0				6,577.0
Tax Savings From Tax Cuts and Jobs Act												$ 201.0
Revenues																						1,512.0	1,298.0
Payments to Acquire Property, Plant, and Equipment																						531.0	626.0
Commonwealth Edison Co [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						41.0
Commonwealth Edison Co [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																								$ 23.0
Public Utilities, Requested Increase (Decrease), Amount																								58.0
Public Utilities, Approved Rate Increase (Decrease), Amount																								$ 35.0
Public Utilities, Requested Equity Capital Structure, Percentage																								6.52%
Public Utilities, Requested Rate Increase (Decrease), Percentage																								8.69%
Public Utilities, Approved Equity Capital Structure, Percentage																								6.52%
Public Utilities, Approved Rate Increase (Decrease), Percentage																								8.69%
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						486.0				410.0
Regulatory Liabilities																						646.0				690.0
Tax Savings From Tax Cuts and Jobs Act			$ 71.0
Revenues																						866.0	796.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																					$ 22.0
Public Utilities, Requested Equity Capital Structure, Percentage																					11.00%
Payments to Acquire Property, Plant, and Equipment																						217.0	201.0
PECO Energy Co [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											$ 4.0
PECO Energy Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											68.0
Public Utilities, Requested Increase (Decrease), Amount			$ 82.0
Public Utilities, Requested Equity Capital Structure, Percentage			10.95%
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						540.0				571.0
Regulatory Liabilities																						1,185.0				1,163.0
Tax Savings From Tax Cuts and Jobs Act											103.0
Revenues																						977.0	951.0
Payments to Acquire Property, Plant, and Equipment																						224.0	206.0
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											31.0
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											$ 72.0
Baltimore Gas and Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						22.0
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						2,960.0				3,047.0
Regulatory Liabilities																						1,965.0				1,928.0
Revenues																						1,251.0	1,175.0
Payments to Acquire Property, Plant, and Equipment																						258.0	320.0
Pepco Holdings LLC [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						19.0
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						863.0				891.0
Regulatory Liabilities																						845.0				832.0
Revenues																						557.0	530.0
Payments to Acquire Property, Plant, and Equipment																						127.0	139.0
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 39.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 3.0
Public Utilities, Requested Increase (Decrease), Amount										$ 11.0			$ 41.0	$ 66.0
Public Utilities, Requested Return on Equity, Percentage														10.10%
Public Utilities, Requested Rate Increase (Decrease), Percentage													10.10%
Potomac Electric Power Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						9.0
Potomac Electric Power Company [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act Through Effective Date		$ 19.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 15.0	$ 24.0
Public Utilities, Requested Return on Equity, Percentage		9.50%
Public Utilities, Requested Rate Increase (Decrease), Percentage	9.50%
Public Utilities, Rate Credit	$ 10.0
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						305.0				314.0
Regulatory Liabilities																						646.0				635.0
Tax Savings From Tax Cuts and Jobs Act								$ 26.0
Revenues																						384.0	362.0
Public Utilities, Requested Return on Equity, Percentage																			10.10%
Public Utilities, Interim Rate Increase (Decrease), Amount																		$ 2.5
Payments to Acquire Property, Plant, and Equipment																						65.0	82.0
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								7.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																	$ 11.0
Public Utilities, Requested Increase (Decrease), Amount																			$ 13.0
Public Utilities, Interim Rate Increase (Decrease), Amount					$ 1.0
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								19.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																$ 19.0		$ 31.0
Public Utilities, Requested Increase (Decrease), Amount																			$ 24.0	$ 27.0
Public Utilities, Approved Rate Increase (Decrease), Amount															$ 13.0
Public Utilities, Requested Return on Equity, Percentage																				10.10%
Public Utilities, Approved Return on Equity, Percentage															9.50%
Public Utilities, Interim Rate Increase (Decrease), Amount					$ 3.0
Delmarva Power and Light Company [Member] | Electric Distribution [Member] | Maryland Service Territory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								$ 13.0		31.0												14.0
Public Utilities, Rate Credit																						2.0
Delmarva Power and Light Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						7.0
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						441.0				430.0
Regulatory Liabilities																						437.0				422.0
Tax Savings From Tax Cuts and Jobs Act							$ 23.0
Revenues																						310.0	275.0
Payments to Acquire Property, Plant, and Equipment																						63.0	$ 88.0
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount				$ 13.0						$ 19.0
Atlantic City Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						3.0
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment																									$ 338.0
Zero Emission Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						8.0				112.0
Zero Emission Standard [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																						202.0
Other Revenue, Net																						150.0
Zero Emission Standard [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						8.0				112.0
Zero Emission Standard [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0.0				0.0
Zero Emission Standard [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0.0				0.0
Zero Emission Standard [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0.0				0.0
Zero Emission Standard [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0.0				0.0
Zero Emission Standard [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0.0				0.0
Zero Emission Standard [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						$ 0.0				$ 0.0