Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) V mi	Dec. 31, 2018 USD ($)
Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi	151.3
Transmission line capacity | V	500
Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi	2.5
Transmission line capacity | V	500
New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V	500
Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	$ 102	$ 103
Accumulated depreciation	53	53
Construction work in progress	$ 0	0
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	75.00%
Plant	$ 1,161	1,131
Accumulated depreciation	627	587
Construction work in progress	$ 13	13
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	50.00%
Plant	$ 1,466	1,451
Accumulated depreciation	571	523
Construction work in progress	$ 21	15
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.59%
Plant	$ 663	648
Accumulated depreciation	249	227
Construction work in progress	$ 53	44
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Nine Mile Point [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	82.00%
Plant	$ 951	910
Accumulated depreciation	156	126
Construction work in progress	$ 27	$ 56
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.55%
PECO Energy Co [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.55%
Delmarva Power & Light Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	1.00%
Delmarva Power & Light Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	7.45%
Atlantic City Electric Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	13.90%
Atlantic City Electric Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	7.45%
Atlantic City Electric Company [Member] | New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	21.78%