Mergers, Acquisitions, and Dispositions Merger Integration Related Costs Table (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
	Mar. 31, 2016	Sep. 30, 2016	Mar. 23, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Business Combination, Integration Related Costs		$ 20		$ 22	$ 123	$ 84
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs		9		10	29	30
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs		0		3	(6)	9
PECO Energy Co [Member]
Business Combination, Integration Related Costs		1		1	3	4
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs		1		2	(3)	4
Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs		3		1	26	3
Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs		2		0	18	2
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs		2		0	17	1
Successor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	$ 63	$ 7
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs			$ 29	$ 3		$ 16
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					13
Regulatory Assets [Member] | Potomac Electric Power Company [Member]
Business Combination, Integration Related Costs					10
Regulatory Assets [Member] | Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs					$ 3