Discontinued Operations - Summarized Results of Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)		$ 5	$ (871)
Loss from discontinued operations, net of tax		(24)	1,239
Income (Loss) from discontinued operations	[1]	(35)	1,188
FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues		54	736
Fuel		(35)	(164)
Purchased power		0	(58)
Other operating expenses		(10)	(369)
Provision for depreciation		0	(63)
General taxes		(4)	(23)
Other expense, net (1)		(2)	(62)
Income (Loss) from discontinued operations, before tax		3	(3)
Income tax expense (benefit)		14	48
Loss from discontinued operations, net of tax		(11)	(51)
Gain (Loss) on disposal of FES and FENOC, net of tax		(24)	1,239	$ 435
Income (Loss) from discontinued operations		$ (35)	$ 1,188

[1] Net of income tax expense (benefits) of $5 million and $(871) million for the three months ended March 31, 2019 and 2018, respectively.