Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Business Acquisition [Line Items]
Business Combination, Bargain Purchase, Gain Recognized, Amount		$ 226	$ 0
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	[1]	1,441
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	[1]	11,088
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets	[1]	5,015
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	[1]	248
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	[1]	21,797
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	[1]	(2,752)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	[1]	(1,515)
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities	[1]	297
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	[1]	5,636
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	[1]	(187)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	[1]	14,655
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	[1]	7,142
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	[1]	4,005
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	[1]	3,447
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations	[1]	821
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets		58
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		278
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	[2]	114
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		1,257
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities		(7)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities		(417)
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities		110
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		(11)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		738
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		519
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent		144
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations		49
Business Combination, Consideration Transferred		293
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets		807
Business Combination, Bargain Purchase, Gain Recognized, Amount		226
Cash and Cash Equivalents [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		110
Business Combination, Consideration Transferred, Other		129
Nuclear Fuel [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other		54
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets		1,700
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets		$ 1,100

[1] Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.

[2] Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 24-Commitments and Contingencies of the Exelon 2016 Form 10-K for additional background regarding SNF obligations to the DOE.