Mergers, Acquisitions, and Dispositions Goodwill Amortization Schedule (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 4,016
Goodwill, Gross	6,688	$ 2,672
Goodwill, Acquired During Period	4,016
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	1,140
Pepco Holdings, LLC [Member]
Goodwill [Line Items]
Goodwill, Gross	4,016
Goodwill, Acquired During Period	$ 4,016