Supplemental Guarantor Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Consolidating Statements of Income
Revenues	[1]	$ 3,869	$ 3,897
OPERATING EXPENSES:
Fuel		381	513
Purchased power		1,124	1,113
Other operating expenses		918	1,057
Provision for depreciation		329	319
General taxes		280	269
Total operating expenses		3,093	3,303
OPERATING INCOME		776	594
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		28	17
Interest expense		(288)	(279)
Capitalized interest		25	34
Total other income (expense)		(235)	(228)
INCOME BEFORE INCOME TAXES		541	366
INCOME TAXES (BENEFITS)		213	144
NET INCOME (LOSS)		328	222
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		328	222
Pension and OPEB prior service costs		(18)	(31)
Amortized gains on derivative hedges		2	1
Change in unrealized gain on available-for-sale securities		28	4
Other comprehensive income (loss)		12	(26)
Income taxes (benefits) on other comprehensive income (loss)		4	(10)
Other comprehensive income (loss), net of tax		8	(16)
COMPREHENSIVE INCOME (LOSS)		336	206
FES
Consolidating Statements of Income
Revenues		1,155	1,332
OPERATING EXPENSES:
Fuel		0	0
Other operating expenses		4	180
Provision for depreciation		3	3
General taxes		8	15
Total operating expenses		1,319	1,698
OPERATING INCOME		(164)	(366)
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		251	241
Capitalized interest		0	0
Total other income (expense)		229	222
INCOME BEFORE INCOME TAXES		65	(144)
INCOME TAXES (BENEFITS)		(66)	(141)
NET INCOME (LOSS)		131	(3)
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		131	(3)
Pension and OPEB prior service costs		(4)	(4)
Amortized gains on derivative hedges			(1)
Change in unrealized gain on available-for-sale securities		23	3
Other comprehensive income (loss)		19	(2)
Income taxes (benefits) on other comprehensive income (loss)		7	(1)
Other comprehensive income (loss), net of tax		12	(1)
COMPREHENSIVE INCOME (LOSS)		143	(4)
FES | Affiliates
OPERATING EXPENSES:
Purchased power		927	957
OTHER INCOME (EXPENSE):
Interest expense		(9)	(6)
FES | Non-Affiliates
OPERATING EXPENSES:
Purchased power		377	543
OTHER INCOME (EXPENSE):
Interest expense		(13)	(13)
FGCO
Consolidating Statements of Income
Revenues		415	493
OPERATING EXPENSES:
Fuel		119	180
Other operating expenses		71	67
Provision for depreciation		31	30
General taxes		10	8
Total operating expenses		231	285
OPERATING INCOME		184	208
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		6	3
Capitalized interest		2	1
Total other income (expense)		(20)	(24)
INCOME BEFORE INCOME TAXES		164	184
INCOME TAXES (BENEFITS)		61	67
NET INCOME (LOSS)		103	117
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		103	117
Pension and OPEB prior service costs		(3)	(4)
Amortized gains on derivative hedges			0
Change in unrealized gain on available-for-sale securities		0	0
Other comprehensive income (loss)		(3)	(4)
Income taxes (benefits) on other comprehensive income (loss)		(1)	(1)
Other comprehensive income (loss), net of tax		(2)	(3)
COMPREHENSIVE INCOME (LOSS)		101	114
FGCO | Affiliates
OPERATING EXPENSES:
Purchased power		0	0
OTHER INCOME (EXPENSE):
Interest expense		(2)	(2)
FGCO | Non-Affiliates
OPERATING EXPENSES:
Purchased power		0	0
OTHER INCOME (EXPENSE):
Interest expense		(26)	(26)
Nuclear Generation Corp
Consolidating Statements of Income
Revenues		531	507
OPERATING EXPENSES:
Fuel		46	50
Other operating expenses		153	154
Provision for depreciation		50	48
General taxes		8	6
Total operating expenses		314	326
OPERATING INCOME		217	181
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		17	14
Capitalized interest		8	8
Total other income (expense)		12	8
INCOME BEFORE INCOME TAXES		229	189
INCOME TAXES (BENEFITS)		86	70
NET INCOME (LOSS)		143	119
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		143	119
Pension and OPEB prior service costs		0	3
Amortized gains on derivative hedges			0
Change in unrealized gain on available-for-sale securities		23	0
Other comprehensive income (loss)		23	3
Income taxes (benefits) on other comprehensive income (loss)		8	1
Other comprehensive income (loss), net of tax		15	2
COMPREHENSIVE INCOME (LOSS)		158	121
Nuclear Generation Corp | Affiliates
OPERATING EXPENSES:
Purchased power		57	68
OTHER INCOME (EXPENSE):
Interest expense		(2)	(1)
Nuclear Generation Corp | Non-Affiliates
OPERATING EXPENSES:
Purchased power		0	0
OTHER INCOME (EXPENSE):
Interest expense		(11)	(13)
Eliminations
Consolidating Statements of Income
Revenues		(902)	(955)
OPERATING EXPENSES:
Fuel		0	0
Other operating expenses		12	12
Provision for depreciation		(1)	(1)
General taxes		0	0
Total operating expenses		(891)	(944)
OPERATING INCOME		(11)	(11)
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		(259)	(245)
Capitalized interest		0	0
Total other income (expense)		(234)	(223)
INCOME BEFORE INCOME TAXES		(245)	(234)
INCOME TAXES (BENEFITS)		1	2
NET INCOME (LOSS)		(246)	(236)
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		(246)	(236)
Pension and OPEB prior service costs		3	1
Amortized gains on derivative hedges			0
Change in unrealized gain on available-for-sale securities		(23)	0
Other comprehensive income (loss)		(20)	1
Income taxes (benefits) on other comprehensive income (loss)		(7)	0
Other comprehensive income (loss), net of tax		(13)	1
COMPREHENSIVE INCOME (LOSS)		(259)	(235)
Eliminations | Affiliates
OPERATING EXPENSES:
Purchased power		(902)	(955)
OTHER INCOME (EXPENSE):
Interest expense		11	7
Eliminations | Non-Affiliates
OPERATING EXPENSES:
Purchased power		0	0
OTHER INCOME (EXPENSE):
Interest expense		14	15
FES
Consolidating Statements of Income
Revenues		1,199	1,377
OPERATING EXPENSES:
Fuel		165	230
Other operating expenses		240	413
Provision for depreciation		83	80
General taxes		26	29
Total operating expenses		973	1,365
OPERATING INCOME		226	12
OTHER INCOME (EXPENSE):
Investment income (loss), including net income from equity investees		15	13
Capitalized interest		10	9
Total other income (expense)		(13)	(17)
INCOME BEFORE INCOME TAXES		213	(5)
INCOME TAXES (BENEFITS)		82	(2)
NET INCOME (LOSS)		131	(3)
OTHER COMPREHENSIVE INCOME (LOSS):
NET INCOME (LOSS)		131	(3)
Pension and OPEB prior service costs		(4)	(4)
Amortized gains on derivative hedges		0	(1)
Change in unrealized gain on available-for-sale securities		23	3
Other comprehensive income (loss)		19	(2)
Income taxes (benefits) on other comprehensive income (loss)		7	(1)
Other comprehensive income (loss), net of tax		12	(1)
COMPREHENSIVE INCOME (LOSS)		143	(4)
FES | Affiliates
OPERATING EXPENSES:
Purchased power		82	70
OTHER INCOME (EXPENSE):
Interest expense		(2)	(2)
FES | Non-Affiliates
OPERATING EXPENSES:
Purchased power		377	543
OTHER INCOME (EXPENSE):
Interest expense		$ (36)	$ (37)
Bruce Mansfield Unit 1
Condensed Financial Statements, Captions [Line Items]
Percentage of undivided interest of non guarantor subsidiary		93.83%

[1] Includes excise tax collections of $107 million and $115 million in the three months ended March 31, 2016 and 2015, respectively.