Supplemental Guarantor Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Consolidating Statements of Income
REVENUES	$ 3,442	$ 3,714	$ 3,309	$ 3,552	$ 3,375	$ 3,917	$ 3,401	$ 3,869	$ 14,017	[1]	$ 14,562	[1]	$ 15,026	[1]
OPERATING EXPENSES:
Fuel									1,383		1,666		1,855
Purchased power									3,194		3,843		4,423
Other operating expenses	1,195	940	956	1,141	1,021	950	963	917	4,232		3,851		3,740
Pension and OPEB mark-to-market adjustment	141	0	0	0	147	0	0	0	141		147		242
Provision for depreciation	293	289	281	275	339	311	334	329	1,138		1,313		1,282
General taxes									1,043		1,042		978
Impairment of assets and related charges	2,244	31	131	0	9,218	0	1,447	0	2,406		10,665		42
Total operating expenses									13,845		22,824		12,734
OPERATING INCOME (LOSS)	(1,830)	884	544	574	(8,924)	861	(975)	776	172		(8,262)		2,292
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									98		84		(22)
Interest expense									(1,178)		(1,157)		(1,132)
Capitalized financing costs									79		103		117
Total other expense									(1,001)		(970)		(1,399)
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									(829)		(9,232)		893
INCOME TAXES (BENEFITS)	413	239	117	126	(3,389)	251	(130)	213	895		(3,055)		315
NET INCOME (LOSS)	(2,499)	396	174	205	(5,796)	380	(1,089)	328	(1,724)		(6,177)		578
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									(85)		(59)		(116)
Amortized gain on derivative hedges									10		8		5
Change in unrealized gain on available-for-sale securities									22		55		(11)
Other comprehensive income (loss)									(53)		4		(122)
Income taxes (benefits) on other comprehensive income (loss)									(21)		1		(47)
Other comprehensive income (loss), net of tax									(32)		3		(75)
Eliminations
Consolidating Statements of Income
REVENUES									(2,363)		(3,587)		(3,758)
OPERATING EXPENSES:
Fuel									0		0		0
Other operating expenses									49		49		49
Pension and OPEB mark-to-market adjustment									0		0		0
Provision for depreciation									(2)		(3)		(3)
General taxes									0		0		0
Impairment of assets and related charges									0		(83)		0
Total operating expenses									(2,316)		(3,624)		(3,712)
OPERATING INCOME (LOSS)									(47)		37		(46)
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									1,806		4,538		(870)
Miscellaneous income									0		0		0
Capitalized financing costs									0		0		0
Total other expense									1,930		4,652		(778)
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									1,883		4,689		(824)
INCOME TAXES (BENEFITS)									27		35		15
NET INCOME (LOSS)									1,856		4,654		(839)
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									13		14		5
Amortized gain on derivative hedges									0		0		0
Change in unrealized gain on available-for-sale securities									(30)		(52)		8
Other comprehensive income (loss)									(17)		(38)		13
Income taxes (benefits) on other comprehensive income (loss)									(5)		(15)		5
Other comprehensive income (loss), net of tax									(12)		(23)		8
COMPREHENSIVE INCOME (LOSS)									1,844		4,631		(831)
Eliminations | Affiliates
OPERATING EXPENSES:
Purchased power									(2,363)		(3,587)		(3,758)
OTHER INCOME (EXPENSE):
Interest expense									68		57		34
Eliminations | Non-Affiliates
OPERATING EXPENSES:
Purchased power									0		0		0
OTHER INCOME (EXPENSE):
Interest expense									56		57		58
FES
Consolidating Statements of Income
REVENUES									3,037		4,242		4,824
OPERATING EXPENSES:
Fuel									0		0		0
Other operating expenses									322		310		378
Pension and OPEB mark-to-market adjustment									(12)		(1)		(8)
Provision for depreciation									12		13		12
General taxes									20		31		45
Impairment of assets and related charges									0		39		21
Total operating expenses									3,458		5,436		5,958
OPERATING INCOME (LOSS)									(421)		(1,194)		(1,134)
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									(1,864)		(4,585)		844
Miscellaneous income									1		4		1
Capitalized financing costs									0		0		0
Total other expense									(1,984)		(4,686)		764
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									(2,405)		(5,880)		(370)
INCOME TAXES (BENEFITS)									(14)		(425)		(452)
NET INCOME (LOSS)									(2,391)		(5,455)		82
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									(14)		(14)		(6)
Amortized gain on derivative hedges									2		0		(3)
Change in unrealized gain on available-for-sale securities									30		52		(9)
Other comprehensive income (loss)									18		38		(18)
Income taxes (benefits) on other comprehensive income (loss)									6		15		(7)
Other comprehensive income (loss), net of tax									12		23		(11)
COMPREHENSIVE INCOME (LOSS)									(2,379)		(5,432)		71
FES | Affiliates
OPERATING EXPENSES:
Purchased power									2,488		4,024		3,826
OTHER INCOME (EXPENSE):
Interest expense									(75)		(50)		(29)
FES | Non-Affiliates
OPERATING EXPENSES:
Purchased power									628		1,020		1,684
OTHER INCOME (EXPENSE):
Interest expense									(46)		(55)		(52)
FG
Consolidating Statements of Income
REVENUES									1,062		1,739		1,801
OPERATING EXPENSES:
Fuel									390		582		679
Other operating expenses									490		286		273
Pension and OPEB mark-to-market adjustment									(30)		(4)		10
Provision for depreciation									32		120		124
General taxes									21		30		26
Impairment of assets and related charges									0		3,937		2
Total operating expenses									903		4,951		1,114
OPERATING INCOME (LOSS)									159		(3,212)		687
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									39		30		17
Miscellaneous income									1		3		2
Capitalized financing costs									2		8		6
Total other expense									(73)		(74)		(87)
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									86		(3,286)		600
INCOME TAXES (BENEFITS)									360		(1,169)		224
NET INCOME (LOSS)									(274)		(2,117)		376
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									(13)		(14)		(5)
Amortized gain on derivative hedges									0		0		0
Change in unrealized gain on available-for-sale securities									0		0		0
Other comprehensive income (loss)									(13)		(14)		(5)
Income taxes (benefits) on other comprehensive income (loss)									(5)		(5)		(2)
Other comprehensive income (loss), net of tax									(8)		(9)		(3)
COMPREHENSIVE INCOME (LOSS)									(282)		(2,126)		373
FG | Affiliates
OPERATING EXPENSES:
Purchased power									0		0		0
OTHER INCOME (EXPENSE):
Interest expense									(11)		(10)		(8)
FG | Non-Affiliates
OPERATING EXPENSES:
Purchased power									0		0		0
OTHER INCOME (EXPENSE):
Interest expense									(104)		(105)		(104)
NG
Consolidating Statements of Income
REVENUES									1,362		2,004		2,138
OPERATING EXPENSES:
Fuel									209		198		192
Other operating expenses									653		632		608
Pension and OPEB mark-to-market adjustment									66		53		55
Provision for depreciation									67		206		191
General taxes									17		27		27
Impairment of assets and related charges									2,031		4,729		10
Total operating expenses									3,119		6,032		1,368
OPERATING INCOME (LOSS)									(1,757)		(4,028)		770
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									113		84		(5)
Miscellaneous income									5		0		0
Capitalized financing costs									24		26		29
Total other expense									97		62		(29)
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									(1,660)		(3,966)		741
INCOME TAXES (BENEFITS)									(78)		(1,429)		278
NET INCOME (LOSS)									(1,582)		(2,537)		463
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									0		0		0
Amortized gain on derivative hedges									0		0		0
Change in unrealized gain on available-for-sale securities									30		52		(8)
Other comprehensive income (loss)									30		52		(8)
Income taxes (benefits) on other comprehensive income (loss)									10		20		(3)
Other comprehensive income (loss), net of tax									20		32		(5)
COMPREHENSIVE INCOME (LOSS)									(1,562)		(2,505)		458
NG | Affiliates
OPERATING EXPENSES:
Purchased power									76		187		285
OTHER INCOME (EXPENSE):
Interest expense									(1)		(4)		(4)
NG | Non-Affiliates
OPERATING EXPENSES:
Purchased power									0		0		0
OTHER INCOME (EXPENSE):
Interest expense									(44)		(44)		(49)
Consolidated
Consolidating Statements of Income
REVENUES	700	743	741	914	997	1,100	1,102	1,199	3,098	[2]	4,398	[2]	5,005	[2]
OPERATING EXPENSES:
Fuel									599		780		871
Other operating expenses	419	291	286	518	352	316	369	240	1,514		1,277		1,308
Pension and OPEB mark-to-market adjustment	24	0	0	0	48	0	0	0	24		48		57
Provision for depreciation	29	28	27	25	86	83	84	83	109		336		324
General taxes									58		88		98
Impairment of assets and related charges	2,031	0	0	0	8,082	0	540	0	2,031		8,622		33
Total operating expenses									5,164		12,795		4,728
OPERATING INCOME (LOSS)	(2,112)	102	61	(117)	(8,153)	101	(571)	226	(2,066)		(8,397)		277
OTHER INCOME (EXPENSE):
Investment income (loss), including net income (loss) from equity investees									94		67		(14)
Miscellaneous income									7		7		3
Capitalized financing costs									26		34		35
Total other expense									(30)		(46)		(130)
INCOME (LOSS) BEFORE INCOME TAXES (BENEFITS)									(2,096)		(8,443)		147
INCOME TAXES (BENEFITS)	281	32	23	(41)	(2,983)	56	(143)	82	295		(2,988)		65
NET INCOME (LOSS)	$ (2,406)	$ 76	$ 19	$ (80)	$ (5,188)	$ 40	$ (438)	$ 131	(2,391)		(5,455)		82
STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension and OPEB prior service costs									(14)		(14)		(6)
Amortized gain on derivative hedges									2		0		(3)
Change in unrealized gain on available-for-sale securities									30		52		(9)
Other comprehensive income (loss)									18		38		(18)
Income taxes (benefits) on other comprehensive income (loss)									6		15		(7)
Other comprehensive income (loss), net of tax									12		23		(11)
COMPREHENSIVE INCOME (LOSS)									(2,379)		(5,432)		71
Consolidated | Affiliates
OPERATING EXPENSES:
Purchased power									201		624		353
OTHER INCOME (EXPENSE):
Interest expense									(19)		(7)		(7)
Consolidated | Non-Affiliates
OPERATING EXPENSES:
Purchased power									628		1,020		1,684
OTHER INCOME (EXPENSE):
Interest expense									$ (138)		$ (147)		$ (147)
Bruce Mansfield Unit 1
Condensed Financial Statements, Captions [Line Items]
Percentage of leasehold interest related to sale leaseback arrangements	93.83%								93.83%

[1] Includes excise tax collections of $390 million, $406 million and $416 million in 2017, 2016 and 2015, respectively.

[2] Includes excise tax collections of $20 million, $28 million and $44 million in 2017, 2016 and 2015, respectively.