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Mergers, Acquisitions and Dispositions - Dispositions Narrative (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
	Feb. 28, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018
Business Dispositions [Line Items]
Assets held for sale		$ 18					$ 904
Liabilities held for sale		11					777
Asset Retirement Obligation, Revision of Estimate		(300)		$ 330		$ 20
Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Assets held for sale		18					904
Liabilities held for sale		11					777
Asset Retirement Obligation, Revision of Estimate		(300)		$ 330		$ 0
Oyster Creek [Member]
Business Dispositions [Line Items]
Assets held for sale							897
Liabilities held for sale							777
Oyster Creek [Member] \| Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Assets held for sale							897
Liabilities held for sale							$ 777
Electrical Contracting Business [Member]
Business Dispositions [Line Items]
Proceeds from Divestiture of Businesses	$ 87
Electrical Contracting Business [Member] \| Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Proceeds from Divestiture of Businesses	$ 87
Operating Expense [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate		(65)
Operating Expense [Member] \| Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate		$ (65)
Operating Expense [Member] \| Oyster Creek [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate			$ 9		$ 84
Operating Expense [Member] \| Oyster Creek [Member] \| Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate			$ 9		$ 84