Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Business Acquisition [Line Items]
Business Combination, Bargain Purchase, Gain Recognized, Amount		$ 0	$ 0	$ 226	$ 0
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred				293
Current assets		58		58
Property, plant and equipment		278		278
Nuclear decommissioning trust funds		807		807
Other assets	[1]	114		114
Total assets		1,257		1,257
Current liabilities		7		7
Asset Retirement Obligations		417		417
Pension and OPEB obligations		49		49
Deferred income taxes		144		144
Spent nuclear fuel obligation		110		110
Other liabilities		11		11
Total liabilities		738		738
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		519		519
Business Combination, Bargain Purchase, Gain Recognized, Amount				226
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				129
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.