Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Mar. 24, 2016	Dec. 31, 2014
Goodwill [Roll Forward]
Goodwill, Gross		$ 8,660	$ 8,660	$ 4,655		$ 4,655
Accumulated impairment loss		1,983	1,983	1,983		1,983
Goodwill, beginning balance	$ 2,672		2,672	2,672
Goodwill from business combination			4,016
Impairment losses			0	0
Goodwill, Purchase Accounting Adjustments			(11)
Goodwill, ending balance		6,677	6,677	2,672
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, Gross		47	47	47		47
Goodwill, beginning balance	47		47	47
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		47	47	47
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, Gross		4,608	4,608	4,608		4,608
Accumulated impairment loss		1,983	1,983	1,983		1,983
Goodwill, beginning balance	2,625		2,625	2,625
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		2,625	2,625	2,625
Delmarva Power and Light Company [Member]
Goodwill [Roll Forward]
Goodwill, Gross		8	8	8		8
Goodwill, beginning balance	8		8	8
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		8	8	8
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	1,418			1,418		1,425
Accumulated impairment loss	12			12		$ 18
Goodwill, beginning balance	1,406	1,406	1,406	1,407
Goodwill from business combination	0		0
Impairment losses	0			(7)
Goodwill, Impairment Loss, Net of Tax				(1)
Goodwill, Other Increase (Decrease)				(6)
Goodwill, ending balance	1,406			$ 1,406
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	0	4,005	4,005
Accumulated impairment loss		0	0		$ 0
Goodwill, beginning balance		0
Goodwill from business combination		4,016
Impairment losses		0
Goodwill, Purchase Accounting Adjustments		(11)
Goodwill, ending balance	$ 0	$ 4,005	$ 4,005