Income Taxes - Unrecognized Tax Benefits That Effect Future Base Rates (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	$ 19	$ 14	$ 214
Commonwealth Edison Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	0
PECO Energy Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	0
Baltimore Gas and Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	1	0	120
Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	14	14	94
Potomac Electric Power Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	59
Delmarva Power & Light Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	21
Atlantic City Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	$ 14	$ 14	$ 14