Discontinued Operations - Summarized Results of Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)		$ (354)		$ 37	$ (1,300)	$ (1)
Income (Loss) from discontinued operations, net of tax					405	0
Income (Loss) from discontinued operations	[1]	(845)		95	370	3
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		83		788	934	2,299
Fuel		(52)		(237)	(269)	(671)
Purchased power		0		(66)	(85)	(189)
Other operating expenses		(24)		(290)	(414)	(1,097)
Provision for depreciation		(18)		(28)	(96)	(80)
General taxes		(4)		(15)	(32)	(74)
Impairment of assets		0		(18)	0	(149)
Other expense, net		(1)		(2)	(82)	(37)
Income (Loss) from discontinued operations, before tax		(16)		132	(44)	2
Income tax expense (benefit)		(5)		37	(9)	(1)
Income (Loss) from discontinued operations, net of tax		(11)		95	(35)	3
Gain (Loss) on disposal of FES and FENOC, net of tax		(834)	$ 1,200	0	405	0
Income (Loss) from discontinued operations		$ (845)		$ 95	370	$ 3
Tax benefit from excess deferred tax liabilities					$ 32

[1] Net of income tax expense (benefit) of $(354) million and $37 million for the three months ended September 30, 2018 and 2017, respectively, and income tax benefits of $(1.3) billion and $(1) million for the nine months ended September 30, 2018 and 2017, respectively.