Mergers, Acquisitions, and Dispositions Merger Integration Related Costs Table (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 23, 2016	Mar. 31, 2015
Business Combination, Integration Related Costs		$ 102		$ 108
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs		16		7
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs		(8)		3
PECO Energy Co [Member]
Business Combination, Integration Related Costs		2		1
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs		2		1
Pepco Holdings, LLC [Member]
Business Combination, Integration Related Costs		27		1
Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs		16		1
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs		13		1
Successor [Member] | Pepco Holdings, LLC [Member]
Business Combination, Integration Related Costs	$ 56
Predecessor [Member] | Pepco Holdings, LLC [Member]
Business Combination, Integration Related Costs			$ 29	$ 8
Regulatory Assets [Member] | Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs		$ 9