Discontinued Operations - Summarized Results (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)		$ 39	$ (16)	$ 44	$ (887)
Loss from discontinued operations, net of tax				(39)	1,239
Income (loss) from discontinued operations	[1]	(29)	(9)	(64)	1,179
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		31	90	85	826
Fuel		(20)	(54)	(55)	(218)
Purchased power		0	(1)	0	(59)
Other operating expenses		(16)	(21)	(26)	(390)
Provision for depreciation		0	(16)	0	(79)
General taxes		(5)	(5)	(9)	(28)
Other income (expense)		10	(18)	8	(80)
Income (loss) from discontinued operations, before tax		0	(25)	3	(28)
Income tax expense (benefit)		14	(16)	28	32
Loss from discontinued operations, net of tax		(14)	(9)	(25)	(60)
Gain (loss) on disposal of FES and FENOC, net of tax		(15)	0	(39)	1,239	$ 435
Income (loss) from discontinued operations		$ (29)	$ (9)	$ (64)	$ 1,179

[1] Net of income tax expense (benefits) of $39 million and $(16) million for the three months ended June 30, 2019 and 2018, respectively, and $44 million and $(887) million for the six months ended June 30, 2019 and 2018, respectively.