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Mergers, Acquisitions and Dispositions - Dispositions Narrative (Details) - USD ($) $ in Millions		3 Months Ended
	Feb. 28, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019
Oyster Creek [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
Operating Expense [Member] \| Oyster Creek [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate		$ 9	$ 84