Regulatory Matters - Narrative (Details) - USD ($) $ in Millions							3 Months Ended		7 Months Ended	9 Months Ended
	Oct. 29, 2019	Jul. 22, 2019	May 23, 2019	Apr. 18, 2019	Feb. 28, 2019	May 01, 2017	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment							$ 1,687	$ 1,690		$ 5,259	$ 5,497
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							80			80
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 22
Public Utilities, Requested Equity Capital Structure, Percentage		10.35%				11.00%
Revenue										8	6
Payments to Acquire Property, Plant, and Equipment										675	615
Increase (Decrease) in Regulatory Assets										62
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 51							5
Revenue			$ (2)							(16)
Payments to Acquire Property, Plant, and Equipment										1,413	1,540
Increase (Decrease) in Regulatory Assets										122
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							52			52
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										(19)
Revenue										(23)
Payments to Acquire Property, Plant, and Equipment										842	667
Increase (Decrease) in Regulatory Liabilities										(90)
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							16			16
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment										1,006	988
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							12			12
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										26
Revenue										11
Payments to Acquire Property, Plant, and Equipment										455	475
Increase (Decrease) in Regulatory Assets										(84)
Increase (Decrease) in Regulatory Liabilities										(71)
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							4			4
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										9
Revenue										(2)
Payments to Acquire Property, Plant, and Equipment				$ 96	$ 338					300	247
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
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										16
Revenue										(1)
Payments to Acquire Property, Plant, and Equipment										245	254
Increase (Decrease) in Regulatory Liabilities										(42)
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
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment										1,282	1,660
Deferred Income Tax Charge [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										95
Deferred Income Tax Charge [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(40)
Deferred Income Tax Charge [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(73)
Deferred Income Tax Charge [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(32)
Deferred Income Tax Charge [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(29)
Removal Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(43)
Clean Energy Legislation [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Competitive businesses other revenues							$ 21			$ 31
Nuclear Plant [Member] | Exelon Generation Co L L C [Member] | Salem [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Interest, percentage							42.59%			42.59%
Generation commodities and services
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax							$ 4,499	4,971		$ 13,436	14,387
Generation commodities and services | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax							4,499	$ 4,970		13,436	$ 14,389
Generation commodities and services | Zero Emission Standard [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									$ 150
License and Service [Member] | Conowingo [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs							41			41
License and Service [Member] | Conowingo [Member] | Subsequent Event [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Environmental Remediation Expense	$ 14
License and Service [Member] | Conowingo [Member] | Subsequent Event [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Environmental Remediation Expense	11
License and Service [Member] | Conowingo [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs							$ 41			41
License and Service [Member] | Conowingo [Member] | Exelon Generation Co L L C [Member] | Subsequent Event [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Environmental Remediation Expense	14
License and Service [Member] | Conowingo [Member] | Exelon Generation Co L L C [Member] | Subsequent Event [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Environmental Remediation Expense	$ 11
Energy Efficiency Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										(34)
Energy Efficiency Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										186
Renewable Energy Program [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										32
Electric Distribution Formula Rate Annual Reconciliations [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										(97)
Under Recovered Energy and Natural Gas Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										(39)
Under Recovered Energy and Natural Gas Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Liabilities										(10)
DC PLUG Charge [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										(26)
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Regulatory Assets										$ (14)