Regulatory Matters - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Regulatory Matters Additional Narrative Information [Line Items]
Competitive businesses other revenues	$ 112	$ 158	$ 421	$ 238
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets	83		83
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			120
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	51		51
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			55
Increase (Decrease) in Regulatory Liabilities			(81)
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	19		19
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	13		13
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	5		5
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	6		6
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(30)
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	2		2
Deferred Income Tax Charge [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(44)
Energy Efficiency Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			25
Nuclear Decommissioning [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(104)
Clean Energy Legislation [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Competitive businesses other revenues	$ 17	$ 10	35	$ 10
Electric Transmission Formula Rate Annual Reconciliations [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			18
Renewable Energy Program [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			17
Energy Efficiency Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			94
Deferred Income Tax Charge [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			$ 54