Mergers, Acquisitions, and Dispositions Goodwill Amortization Schedule (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 23, 2016	Sep. 30, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill		$ 6,672	$ 2,672
Goodwill, Acquired During Period	$ 4,016	(16)
Goodwill, Other Increase (Decrease)		(16)
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill		47	47
Pepco Holdings LLC [Member]
Goodwill [Line Items]
Goodwill		4,000	$ 0
Goodwill, Acquired During Period	$ 4,016
Goodwill, Other Increase (Decrease)		$ (16)