Fair Value Measurements (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets
Fair value, assets	$ 3,197	$ 2,876
Liabilities
Fair value, liabilities	(238)	(281)
Net assets (liabilities)	2,959	2,595
FES
Assets
Fair value, assets	1,766	1,559
Liabilities
Fair value, liabilities	(129)	(142)
Net assets (liabilities)	1,637	1,417
Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(124)	(131)
Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(124)	(131)
FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	(6)	(13)
FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(5)	(11)
NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(108)	(137)
Corporate debt securities
Assets
Fair value, assets	1,247	1,245
Corporate debt securities | FES
Assets
Fair value, assets	726	678
Commodity contracts | Derivative Assets
Assets
Fair value, assets	210	228
Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	210	228
FTRs | Derivative Assets
Assets
Fair value, assets	7	8
FTRs | Derivative Assets | FES
Assets
Fair value, assets	4	5
NUG contracts | Derivative Assets
Assets
Fair value, assets	1	1
Equity securities
Assets
Fair value, assets	925	576
Equity securities | FES
Assets
Fair value, assets	634	378
Foreign government debt securities
Assets
Fair value, assets	78	75
Foreign government debt securities | FES
Assets
Fair value, assets	58	59
U.S. government debt securities
Assets
Fair value, assets	161	180
U.S. government debt securities | FES
Assets
Fair value, assets	48	23
U.S. state debt securities
Assets
Fair value, assets	246	246
U.S. state debt securities | FES
Assets
Fair value, assets	3	4
Other
Assets
Fair value, assets	322	317
Other | FES
Assets
Fair value, assets	83	184
Level 1
Assets
Fair value, assets	1,134	685
Liabilities
Fair value, liabilities	(6)	(9)
Net assets (liabilities)	1,128	676
Level 1 | FES
Assets
Fair value, assets	646	382
Liabilities
Fair value, liabilities	(6)	(9)
Net assets (liabilities)	640	373
Level 1 | Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(6)	(9)
Level 1 | Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(6)	(9)
Level 1 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Level 1 | FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	0	0
Level 1 | NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Level 1 | Corporate debt securities
Assets
Fair value, assets	0	0
Level 1 | Corporate debt securities | FES
Assets
Fair value, assets	0	0
Level 1 | Commodity contracts | Derivative Assets
Assets
Fair value, assets	10	4
Level 1 | Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	10	4
Level 1 | FTRs | Derivative Assets
Assets
Fair value, assets	0	0
Level 1 | FTRs | Derivative Assets | FES
Assets
Fair value, assets	0	0
Level 1 | NUG contracts | Derivative Assets
Assets
Fair value, assets	0	0
Level 1 | Equity securities
Assets
Fair value, assets	925	576
Level 1 | Equity securities | FES
Assets
Fair value, assets	634	378
Level 1 | Foreign government debt securities
Assets
Fair value, assets	0	0
Level 1 | Foreign government debt securities | FES
Assets
Fair value, assets	0	0
Level 1 | U.S. government debt securities
Assets
Fair value, assets	0	0
Level 1 | U.S. government debt securities | FES
Assets
Fair value, assets	0	0
Level 1 | U.S. state debt securities
Assets
Fair value, assets	0	0
Level 1 | U.S. state debt securities | FES
Assets
Fair value, assets	0	0
Level 1 | Other
Assets
Fair value, assets	199	105
Level 1 | Other | FES
Assets
Fair value, assets	2	0
Level 2
Assets
Fair value, assets	2,055	2,182
Liabilities
Fair value, liabilities	(118)	(122)
Net assets (liabilities)	1,937	2,060
Level 2 | FES
Assets
Fair value, assets	1,116	1,172
Liabilities
Fair value, liabilities	(118)	(122)
Net assets (liabilities)	998	1,050
Level 2 | Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(118)	(122)
Level 2 | Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(118)	(122)
Level 2 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Level 2 | FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	0	0
Level 2 | NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Level 2 | Corporate debt securities
Assets
Fair value, assets	1,247	1,245
Level 2 | Corporate debt securities | FES
Assets
Fair value, assets	726	678
Level 2 | Commodity contracts | Derivative Assets
Assets
Fair value, assets	200	224
Level 2 | Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	200	224
Level 2 | FTRs | Derivative Assets
Assets
Fair value, assets	0	0
Level 2 | FTRs | Derivative Assets | FES
Assets
Fair value, assets	0	0
Level 2 | NUG contracts | Derivative Assets
Assets
Fair value, assets	0	0
Level 2 | Equity securities
Assets
Fair value, assets	0	0
Level 2 | Equity securities | FES
Assets
Fair value, assets	0	0
Level 2 | Foreign government debt securities
Assets
Fair value, assets	78	75
Level 2 | Foreign government debt securities | FES
Assets
Fair value, assets	58	59
Level 2 | U.S. government debt securities
Assets
Fair value, assets	161	180
Level 2 | U.S. government debt securities | FES
Assets
Fair value, assets	48	23
Level 2 | U.S. state debt securities
Assets
Fair value, assets	246	246
Level 2 | U.S. state debt securities | FES
Assets
Fair value, assets	3	4
Level 2 | Other
Assets
Fair value, assets	123	212
Level 2 | Other | FES
Assets
Fair value, assets	81	184
Level 3
Assets
Fair value, assets	8	9
Liabilities
Fair value, liabilities	(114)	(150)
Net assets (liabilities)	(106)	(141)
Level 3 | FES
Assets
Fair value, assets	4	5
Liabilities
Fair value, liabilities	(5)	(11)
Net assets (liabilities)	(1)	(6)
Level 3 | Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Level 3 | Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	0	0
Level 3 | FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	(6)	(13)
Level 3 | FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(5)	(11)
Level 3 | NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(108)	(137)
Level 3 | Corporate debt securities
Assets
Fair value, assets	0	0
Level 3 | Corporate debt securities | FES
Assets
Fair value, assets	0	0
Level 3 | Commodity contracts | Derivative Assets
Assets
Fair value, assets	0	0
Level 3 | Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	0	0
Level 3 | FTRs | Derivative Assets
Assets
Fair value, assets	7	8
Level 3 | FTRs | Derivative Assets | FES
Assets
Fair value, assets	4	5
Level 3 | NUG contracts | Derivative Assets
Assets
Fair value, assets	1	1
Level 3 | Equity securities
Assets
Fair value, assets	0	0
Level 3 | Equity securities | FES
Assets
Fair value, assets	0	0
Level 3 | Foreign government debt securities
Assets
Fair value, assets	0	0
Level 3 | Foreign government debt securities | FES
Assets
Fair value, assets	0	0
Level 3 | U.S. government debt securities
Assets
Fair value, assets	0	0
Level 3 | U.S. government debt securities | FES
Assets
Fair value, assets	0	0
Level 3 | U.S. state debt securities
Assets
Fair value, assets	0	0
Level 3 | U.S. state debt securities | FES
Assets
Fair value, assets	0	0
Level 3 | Other
Assets
Fair value, assets	0	0
Level 3 | Other | FES
Assets
Fair value, assets	$ 0	$ 0