Mergers, Acquisitions and Dispositions Goodwill Amortization Schedule (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Mar. 24, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill, Gross		$ 8,660		$ 4,655	$ 4,655
Goodwill		6,677		$ 2,672	$ 2,672
Goodwill, Acquired During Period		4,016
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			$ 4,005
Pepco Holdings LLC [Member]
Goodwill [Line Items]
Goodwill, Other Increase (Decrease)	[1]	$ (11)
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			$ 1,200

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