Maximum basis points that can be added to the average rate on 30-year treasury notes, to determine the allowed ROE for ComEd's revenue requirement.

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[Line Items] for Schedule of Energy Efficiency Formula Rate Updates [Table]

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved return on equity.

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Percentage of public utility's requested equity to capital, including debt and equity.

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Amount of public utility's amended requested rate increase (decrease) with regulatory agency.

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Regulatory Matters - Energy Efficiency Formula Rate (Details) $ in Millions					3 Months Ended		12 Months Ended
	Dec. 04, 2019 USD ($)	Nov. 26, 2019 USD ($)	May 23, 2019 USD ($)	Dec. 04, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 4	$ 24
Commonwealth Edison Co [Member]
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 50					$ 53	$ (3)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 51				$ 5
Public Utilities, Requested Equity Capital Structure, Percentage			6.51%
Public Utilities, Approved Return on Equity, Percentage		8.91%					11.50%
Basis points for ComEd's Revenue Requirement			580
Electric Distribution [Member] \| Commonwealth Edison Co [Member]
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ (17)			$ (24)				$ (68)	$ 34
Public Utilities, Approved Return on Equity, Percentage	8.91%			8.69%
Basis points for ComEd's Revenue Requirement							580	580