Discontinued Operations - Summarized Results (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)		$ 2	$ (342)	$ 46	$ (1,200)
Loss from discontinued operations, net of tax				(16)	405
Income (loss) from discontinued operations	[1]	2	(857)	(62)	322
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		62	83	147	934
Fuel		(50)	(52)	(105)	(269)
Purchased power		0	0	0	(85)
Other operating expenses		(16)	(24)	(42)	(414)
Provision for depreciation		0	(18)	0	(96)
General taxes		(2)	(4)	(11)	(32)
Other income (expense)		2	(1)	10	(82)
Loss from discontinued operations, before tax		(4)	(16)	(1)	(44)
Income tax expense (benefit)		17	7	45	39
Loss from discontinued operations, net of tax		(21)	(23)	(46)	(83)
Gain (loss) on disposal of FES and FENOC, net of tax		23	(834)	(16)	405	$ 435
Income (loss) from discontinued operations		$ 2	$ (857)	$ (62)	$ 322

[1] Net of income tax expense (benefits) of $2 million and $(342) million for the three months ended September 30, 2019 and 2018, respectively, and $46 million and $(1.2) billion for the nine months ended September 30, 2019 and 2018, respectively.