Property, Plant and Equipment - Summary of Capitalized Interest and AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	$ 22	$ 24	$ 31
Allowance for Funds Used During Construction, Capitalized Interest	150	132	109
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	22	24	31
Allowance for Funds Used During Construction, Capitalized Interest	0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	42	32	30
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	23	17	12
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	30	29	24
Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	55	54	44
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	42	39	34
Delmarva Power & Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	6	6	4
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	$ 7	$ 9	$ 4