Commitments and Contingencies Merger Commitment (Details) $ in Millions	3 Months Ended
	Jun. 30, 2018 USD ($) MGPSite MW	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,368
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,745
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	$ 39
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Mgp Site Contingency Count | MGPSite	2
Other Commitment	$ 13
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	9
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	513	$ 0
Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	122
Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	140
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	76
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	84
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	67
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	7
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	315
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 95
Wind Assets [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
OtherNonFinancialCommitment1 | MW	100
Purchase Commitment | MW	120
Other Solar Projects [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
OtherNonFinancialCommitment1 | MW	27
Business Acquisition, Expected New Generation Mwh | MW	37
Minimum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	285
Maximum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	300
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Mutual Property Insurance Distribution To Members	$ 31