Regulatory Matters - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Aug. 26, 2020
Regulatory Matters Additional Narrative Information [Line Items]
COVID-19 Regulatory Asset	$ 60		$ 60
Competitive businesses other revenues	132	$ 194	552	$ 432
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			255
COVID-19 Regulatory Asset	18		18
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			135
COVID-19 Regulatory Asset	20		20
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
COVID-19 Regulatory Asset	11		11
Increase (Decrease) in Regulatory Liabilities			(68)
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
COVID-19 Regulatory Asset	11		11
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
COVID-19 Regulatory Asset	8		8
Increase (Decrease) in Regulatory Liabilities			(58)
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
COVID-19 Regulatory Asset	3		3
Increase (Decrease) in Regulatory Liabilities			(49)
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure					$ 220
Increase (Decrease) in Regulatory Assets			58
COVID-19 Regulatory Asset	$ 0		0
Increase (Decrease) in Regulatory Liabilities			(55)
Deferred Income Tax Charge [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(73)
Deferred Income Tax Charge [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(99)
Deferred Income Tax Charge [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(54)
Deferred Income Tax Charge [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(80)
Removal Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(4)
Clean Energy Legislation [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Competitive businesses other revenues			56	$ 31
Electric Transmission Formula Rate Annual Reconciliations [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			24
Electric Transmission Formula Rate Annual Reconciliations [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			16
Electric Transmission Formula Rate Annual Reconciliations [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			13
electric energy and natural gas cost [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			24
electric energy and natural gas cost [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			(3)
Securitized Stranded Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities			9
Energy Efficiency Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			145
Deferred Income Tax Charge [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			119
Deferred Storm Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			29
Uncollectible Deferral [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			19
Electric Energy Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			17
Securitized Stranded Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			(9)
Electric Distribution Formula Rate One-time Events [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			58
Electric Distribution Formula Rate Annual Reconciliations [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			(37)
Asset Retirement Obligation Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets			$ 47