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Fair Value Measurements (Details 1) - Level 3 - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2016 | Dec. 31, 2015
NUG contracts |  |
Reconciliation of changes in the fair value of FTRs contracts |  |
Beginning Balance, Derivative Assets | $ 1 | $ 2
Beginning Balance, Derivative Liabilities | (137) | (153)
Beginning Balance, Net | (136) | (151)
Unrealized gain (loss), Derivative Assets | 0 | 2
Unrealized gain (loss), Derivative Liabilities | (11) | (49)
Unrealized gain (loss), Net | (11) | (47)
Purchases, Derivative Assets | 0 | 0
Purchases, Derivative Liabilities | 0 | 0
Purchases, Net | 0 | 0
Settlements, Derivative Assets | 0 | (3)
Settlements, Derivative Liabilities | 24 | 65
Settlements, Net | 24 | 62
Ending Balance, Derivative Assets | 1 | 1
Ending Balance, Derivative Liabilities | (124) | (137)
Ending Balance, Net | (123) | (136)
FTRs |  |
Reconciliation of changes in the fair value of FTRs contracts |  |
Beginning Balance, Derivative Assets | 8 | 39
Beginning Balance, Derivative Liabilities | (13) | (14)
Beginning Balance, Net | (5) | 25
Unrealized gain (loss), Derivative Assets | 0 | (5)
Unrealized gain (loss), Derivative Liabilities | (1) | (7)
Unrealized gain (loss), Net | (1) | (12)
Purchases, Derivative Assets | 15 | 22
Purchases, Derivative Liabilities | (7) | (11)
Purchases, Net | 8 | 11
Settlements, Derivative Assets | (6) | (48)
Settlements, Derivative Liabilities | 13 | 19
Settlements, Net | 7 | (29)
Ending Balance, Derivative Assets | 17 | 8
Ending Balance, Derivative Liabilities | (8) | (13)
Ending Balance, Net | 9 | (5)
FTRs | FES |  |
Reconciliation of changes in the fair value of FTRs contracts |  |
Beginning Balance, Derivative Assets | 5 | 27
Beginning Balance, Derivative Liabilities | (11) | (13)
Beginning Balance, Net | (6) | 14
Unrealized gain (loss), Derivative Assets | 0 | 2
Unrealized gain (loss), Derivative Liabilities | (1) | (5)
Unrealized gain (loss), Net | (1) | (3)
Purchases, Derivative Assets | 9 | 9
Purchases, Derivative Liabilities | (4) | (10)
Purchases, Net | 5 | (1)
Settlements, Derivative Assets | (2) | (33)
Settlements, Derivative Liabilities | 11 | 17
Settlements, Net | 9 | (16)
Ending Balance, Derivative Assets | 12 | 5
Ending Balance, Derivative Liabilities | (5) | (11)
Ending Balance, Net | $ 7 | $ (6)

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