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Fair Value Measurements (Details 1) - Level 3 - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015
NUG contracts |  |
Reconciliation of changes in the fair value of NUG contracts |  |
Beginning Balance, Derivative Assets | $ 1 | $ 2
Beginning Balance, Derivative Liabilities | (137) | (153)
Beginning Balance, Net | (136) | (151)
Unrealized gain (loss), Derivative Assets | 2 | 2
Unrealized gain (loss), Derivative Liabilities | (17) | (49)
Unrealized gain (loss), Net | (15) | (47)
Purchases, Derivative Assets | 0 | 0
Purchases, Derivative Liabilities | 0 | 0
Purchases, Net | 0 | 0
Settlements, Derivative Assets | (2) | (3)
Settlements, Derivative Liabilities | 46 | 65
Settlements, Net | 44 | 62
Ending Balance, Derivative Assets | 1 | 1
Ending Balance, Derivative Liabilities | (108) | (137)
Ending Balance, Net | (107) | (136)
FTRs |  |
Reconciliation of changes in the fair value of NUG contracts |  |
Beginning Balance, Derivative Assets | 8 | 39
Beginning Balance, Derivative Liabilities | (13) | (14)
Beginning Balance, Net | (5) | 25
Unrealized gain (loss), Derivative Assets | (6) | (5)
Unrealized gain (loss), Derivative Liabilities | (4) | (7)
Unrealized gain (loss), Net | (10) | (12)
Purchases, Derivative Assets | 16 | 22
Purchases, Derivative Liabilities | (7) | (11)
Purchases, Net | 9 | 11
Settlements, Derivative Assets | (11) | (48)
Settlements, Derivative Liabilities | 18 | 19
Settlements, Net | 7 | (29)
Ending Balance, Derivative Assets | 7 | 8
Ending Balance, Derivative Liabilities | (6) | (13)
Ending Balance, Net | 1 | (5)
FES | FTRs |  |
Reconciliation of changes in the fair value of NUG contracts |  |
Beginning Balance, Derivative Assets | 5 | 27
Beginning Balance, Derivative Liabilities | (11) | (13)
Beginning Balance, Net | (6) | 14
Unrealized gain (loss), Derivative Assets | (4) | 2
Unrealized gain (loss), Derivative Liabilities | (3) | (5)
Unrealized gain (loss), Net | (7) | (3)
Purchases, Derivative Assets | 10 | 9
Purchases, Derivative Liabilities | (5) | (10)
Purchases, Net | 5 | (1)
Settlements, Derivative Assets | (7) | (33)
Settlements, Derivative Liabilities | 14 | 17
Settlements, Net | 7 | (16)
Ending Balance, Derivative Assets | 4 | 5
Ending Balance, Derivative Liabilities | (5) | (11)
Ending Balance, Net | $ (1) | $ (6)

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