Mergers, Acquisitions and Dispositions - Purchase Price Allocation of Merger with Constellation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2014	Sep. 01, 2016	Mar. 24, 2016	Mar. 23, 2016
Business Acquisition [Line Items]
Current assets				$ 1,441
Property, plant and equipment				11,088
Total assets				21,797
Current liabilities				2,752
Unamortized energy contract liabilities				(1,515)
Other liabilities				(187)
Total liabilities				(14,655)
Total net assets				7,142
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations				821
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent				3,447
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			$ 4,005
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets				5,015
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets				248
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities				297
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt				$ 5,636
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Current assets	$ 390
Unamortized energy contracts	115
Current liabilities	(196)
Unamortized energy contract liabilities	110
Other liabilities	(57)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	(16)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	50
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets	184
ConEdision [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Current assets		$ 204
Property, plant and equipment		2
Unamortized energy contracts		6
Total assets		322
Unamortized energy contract liabilities		(65)
Total liabilities		(65)
Total net assets		257
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets		9
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets		100
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets		$ 1
Integrys [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Total net assets	360
Business Combination, Bargain Purchase, Gain Recognized, Amount	28
Business Combination, Consideration Transferred	$ 332