Regulatory Matters - Schedule of Completed Rate Cases (Details) $ in Millions																		3 Months Ended		12 Months Ended
	Dec. 17, 2019 USD ($)	Dec. 05, 2019 USD ($)	Dec. 04, 2019 USD ($)	Nov. 26, 2019 USD ($)	Aug. 12, 2019 USD ($)	May 23, 2019 USD ($)	May 16, 2019 USD ($)	Apr. 08, 2019 USD ($)	Mar. 13, 2019 USD ($)	Jan. 04, 2019 USD ($)	Dec. 20, 2018 USD ($)	Dec. 04, 2018 USD ($)	Nov. 19, 2018 USD ($)	Oct. 12, 2018 USD ($)	Apr. 16, 2018 USD ($)	Mar. 29, 2018 USD ($)	Jun. 27, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																		$ 4	$ 24
Commonwealth Edison Co [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 21
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 51														5
Public Utilities, Approved Rate Increase (Decrease), Amount				$ 50																$ 53	$ (3)
Public Utilities, Approved Return on Equity, Percentage				8.91%																11.50%
Basis points for ComEd's Revenue Requirement						580
Public Utilities, Approved Equity Capital Structure, Percentage																				8.21%
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount								$ (6)							$ (23)
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
Public Utilities, Approved Equity Capital Structure, Percentage																				6.51%	6.52%
Public Utilities, Interim Rate Increase (Decrease), Amount																				$ 51	$ (58)
PECO Energy Co [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 14															$ 22
Public Utilities, Approved Equity Capital Structure, Percentage		7.62%
PECO Energy Co [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																$ 82
Public Utilities, Approved Rate Increase (Decrease), Amount											$ 25
Baltimore Gas and Electric Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				(10)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ (19)
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.35%
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 59
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 45
Public Utilities, Approved Return on Equity, Percentage	9.75%
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 74													$ 61
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 18									$ 43
Public Utilities, Approved Return on Equity, Percentage	9.70%									9.80%
Atlantic City Electric Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 11
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ 9
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.79%
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount													$ 122
Public Utilities, Approved Rate Increase (Decrease), Amount									$ 70
Public Utilities, Approved Return on Equity, Percentage									9.60%
Potomac Electric Power Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 15
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ 26
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.75%
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 27
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 10
Public Utilities, Approved Return on Equity, Percentage					9.60%