Intangible Assets - Schedule of Goodwill (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, Gross		$ 8,660,000,000	$ 8,660,000,000	$ 8,660,000,000		$ 4,655,000,000
Accumulated impairment loss		1,983,000,000	1,983,000,000	1,983,000,000		1,983,000,000
Goodwill, beginning balance	$ 2,672,000,000		6,677,000,000	2,672,000,000
Goodwill from business combination			0	4,016,000,000
Impairment losses			0	0
Goodwill, Purchase Accounting Adjustments				(11,000,000)
Goodwill, ending balance		6,677,000,000	6,677,000,000	6,677,000,000
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, Gross		47,000,000	47,000,000	47,000,000		47,000,000
Goodwill, beginning balance	47,000,000		47,000,000	47,000,000
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		47,000,000	47,000,000	47,000,000
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, Gross		4,608,000,000	4,608,000,000	4,608,000,000		4,608,000,000
Accumulated impairment loss		1,983,000,000	1,983,000,000	1,983,000,000		1,983,000,000
Goodwill, beginning balance	2,625,000,000		2,625,000,000	2,625,000,000
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		2,625,000,000	2,625,000,000	2,625,000,000
Delmarva Power and Light Company [Member]
Goodwill [Roll Forward]
Goodwill, Gross		8,000,000	8,000,000	8,000,000		8,000,000
Goodwill, beginning balance	8,000,000		8,000,000	8,000,000
Impairment losses			0	0
Goodwill, ending balance		8,000,000	8,000,000	8,000,000
Pepco Holdings LLC [Member]
Goodwill [Roll Forward]
Goodwill from business combination			0
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	1,418,000,000					1,418,000,000
Accumulated impairment loss	12,000,000					$ 12,000,000
Goodwill, beginning balance	1,406,000,000	1,406,000,000		1,406,000,000
Goodwill from business combination	0
Impairment losses	0
Goodwill, ending balance	1,406,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	0	4,005,000,000	4,005,000,000	4,005,000,000
Accumulated impairment loss		0	0	0	$ 0
Goodwill, beginning balance		0	4,005,000,000
Goodwill from business combination		4,016,000,000	0
Impairment losses		0	0
Goodwill, Purchase Accounting Adjustments		(11,000,000)	0
Goodwill, ending balance	$ 0	$ 4,005,000,000	$ 4,005,000,000	$ 4,005,000,000