Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	$ 1,441
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	11,088
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets	5,015
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	248
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	21,792
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	2,752
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	(1,515)
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities	297
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	5,636
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	187
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	(14,650)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	7,142
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	4,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	3,442
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations	821
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	204
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	322
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	(65)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	(65)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	257
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	100
Business Combination, Consideration Transferred	257
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Assets	6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	1
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	1,683
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 1,128