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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

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