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Fair Value Measurements (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Fair value, assets	$ 3,579	$ 3,197
Liabilities
Fair value, liabilities	(107)	(238)
Net assets (liabilities)	3,472	2,959
FES
Assets
Fair value, assets	1,888	1,766
Liabilities
Fair value, liabilities	(24)	(129)
Net assets (liabilities)	1,864	1,637
Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(27)	(124)
Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(23)	(124)
FTRs | Derivative Liabilities
Liabilities
Fair value, liabilities	(1)	(6)
FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(1)	(5)
NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(79)	(108)
Corporate debt securities
Assets
Fair value, assets	1,196	1,247
Corporate debt securities | FES
Assets
Fair value, assets	720	726
Commodity contracts | Derivative Assets
Assets
Fair value, assets	33	210
Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	33	210
FTRs | Derivative Assets
Assets
Fair value, assets	4	7
FTRs | Derivative Assets | FES
Assets
Fair value, assets	1	4
NUG contracts | Derivative Assets
Assets
Fair value, assets	0	1
Equity securities
Assets
Fair value, assets	1,104	925
Equity securities | FES
Assets
Fair value, assets	810	634
Foreign government debt securities
Assets
Fair value, assets	88	78
Foreign government debt securities | FES
Assets
Fair value, assets	65	58
U.S. government debt securities
Assets
Fair value, assets	154	161
U.S. government debt securities | FES
Assets
Fair value, assets	133	48
U.S. state debt securities
Assets
Fair value, assets	276	246
U.S. state debt securities | FES
Assets
Fair value, assets	29	3
Other
Assets
Fair value, assets	724	322
Other | FES
Assets
Fair value, assets	97	83
Level 1
Assets
Fair value, assets	1,693	1,134
Liabilities
Fair value, liabilities	0	(6)
Net assets (liabilities)	1,693	1,128
Level 1 | FES
Assets
Fair value, assets	811	646
Liabilities
Fair value, liabilities	0	(6)
Net assets (liabilities)	811	640
Level 1 | Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	0	(6)
Level 1 | Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	0	(6)
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	0	10
Level 1 | Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	0	10
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	1,104	925
Level 1 | Equity securities | FES
Assets
Fair value, assets	810	634
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	589	199
Level 1 | Other | FES
Assets
Fair value, assets	1	2
Level 2
Assets
Fair value, assets	1,882	2,055
Liabilities
Fair value, liabilities	(27)	(118)
Net assets (liabilities)	1,855	1,937
Level 2 | FES
Assets
Fair value, assets	1,076	1,116
Liabilities
Fair value, liabilities	(23)	(118)
Net assets (liabilities)	1,053	998
Level 2 | Commodity contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(27)	(118)
Level 2 | Commodity contracts | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(23)	(118)
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	1,196	1,247
Level 2 | Corporate debt securities | FES
Assets
Fair value, assets	720	726
Level 2 | Commodity contracts | Derivative Assets
Assets
Fair value, assets	33	200
Level 2 | Commodity contracts | Derivative Assets | FES
Assets
Fair value, assets	33	200
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	88	78
Level 2 | Foreign government debt securities | FES
Assets
Fair value, assets	65	58
Level 2 | U.S. government debt securities
Assets
Fair value, assets	154	161
Level 2 | U.S. government debt securities | FES
Assets
Fair value, assets	133	48
Level 2 | U.S. state debt securities
Assets
Fair value, assets	276	246
Level 2 | U.S. state debt securities | FES
Assets
Fair value, assets	29	3
Level 2 | Other
Assets
Fair value, assets	135	123
Level 2 | Other | FES
Assets
Fair value, assets	96	81
Level 3
Assets
Fair value, assets	4	8
Liabilities
Fair value, liabilities	(80)	(114)
Net assets (liabilities)	(76)	(106)
Level 3 | FES
Assets
Fair value, assets	1	4
Liabilities
Fair value, liabilities	(1)	(5)
Net assets (liabilities)	0	(1)
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	(1)	(6)
Level 3 | FTRs | Derivative Liabilities | FES
Liabilities
Fair value, liabilities	(1)	(5)
Level 3 | NUG contracts | Derivative Liabilities
Liabilities
Fair value, liabilities	(79)	(108)
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	4	7
Level 3 | FTRs | Derivative Assets | FES
Assets
Fair value, assets	1	4
Level 3 | NUG contracts | Derivative Assets
Assets
Fair value, assets	0	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

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Fair value of assets and liabilities net.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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