Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 7,269	$ 6,932	$ 6,814	$ 7,699	$ 7,375	$ 3,925	$ 6,814	$ 3,925
Other comprehensive income before reclassifications								(97)
Amounts reclassified from AOCI	(7)			(16)			(20)	(50)
Deconsolidation of FES and FENOC								5
Other comprehensive loss	(7)			(16)			(20)	(142)
Income taxes (benefits) on other comprehensive income (loss)	(3)			(4)			(6)	(61)
Other comprehensive loss, net of tax	(4)	(5)	(5)	(12)	(13)	(56)	(14)	(81)
Ending balance	7,272	7,269	6,932	6,873	7,699	7,375	7,272	6,873
Gains & Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(10)		(11)				(11)
Amounts reclassified from AOCI	0						1
Other comprehensive loss	0						1
Income taxes (benefits) on other comprehensive income (loss)	0						0
Other comprehensive loss, net of tax	0						1
Ending balance	(10)	(10)					(10)
Gains & Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				(14)		(22)		(22)
Other comprehensive income before reclassifications								0
Amounts reclassified from AOCI				2				6
Deconsolidation of FES and FENOC								13
Other comprehensive loss				2				19
Income taxes (benefits) on other comprehensive income (loss)				0				9
Other comprehensive loss, net of tax				2				10
Ending balance				(12)	(14)			(12)
Unrealized Gains on AFS Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0		0	0		67	0	67
Other comprehensive income before reclassifications								(97)
Amounts reclassified from AOCI	0			0			0	(1)
Deconsolidation of FES and FENOC								(8)
Other comprehensive loss	0			0			0	(106)
Income taxes (benefits) on other comprehensive income (loss)	0			0			0	(39)
Other comprehensive loss, net of tax	0			0			0	(67)
Ending balance	0	0		0	0		0	0
Defined Benefit Pension & OPEB Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	41		52	87		97	52	97
Other comprehensive income before reclassifications								0
Amounts reclassified from AOCI	(7)			(18)			(21)	(55)
Deconsolidation of FES and FENOC								0
Other comprehensive loss	(7)			(18)			(21)	(55)
Income taxes (benefits) on other comprehensive income (loss)	(3)			(4)			(6)	(31)
Other comprehensive loss, net of tax	(4)			(14)			(15)	(24)
Ending balance	37	41		73	87		37	73
AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	31	36	41	73	86	142	41	142
Other comprehensive loss, net of tax	(4)	(5)	(5)	(12)	(13)	(56)
Ending balance	$ 27	$ 31	$ 36	$ 61	$ 73	$ 86	$ 27	$ 61