Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
		Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Business Combination, Bargain Purchase, Gain Recognized, Amount			$ 7	$ 0	$ 233	$ 0
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 289
Current assets		60
Property, plant and equipment		298
Nuclear decommissioning trust funds		807
Other assets	[1]	114
Total assets		1,279
Current liabilities		6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities		444
Pension and OPEB obligations		33
Deferred income taxes		149
Spent nuclear fuel obligation		110
Other liabilities		15
Total liabilities		757
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		522
Business Combination, Bargain Purchase, Gain Recognized, Amount			7		233
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets			$ 110		$ 110
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		110
Business Combination, Consideration Transferred, Other		125
Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other		$ 54

[1] 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.