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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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