Mergers, Acquisitions, and Dispositions Merger Integration Related Costs Table (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Business Combination, Integration Related Costs		$ 1		$ (87)	$ 103	$ 21
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs		4		7	20	15
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs		1		3	(7)	6
PECO Energy Co [Member]
Business Combination, Integration Related Costs		1		1	2	2
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs		(5)		1	(4)	3
Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs		(4)		1	23	2
Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs		0		1	16	1
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs		2		1	15	1
Successor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	$ 55	$ (1)
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs			$ 29	$ 5		$ 14
Regulatory Assets [Member] | Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs					8
Regulatory Assets [Member] | Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs					6
Regulatory Assets [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs					12
Regulatory Assets [Member] | Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs					$ 3