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COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Millions, $ in Millions | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2018 CAD ($) | Jan. 01, 2018 USD ($) | Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items] |  |  |  |
Loans to and accounts receivable from the Canadian Entities | $ 0.0 |  | $ 51.6 | $ 51.6
Cash contribution |  | $ 19.0 |  |
Michigan Electricity Matters [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Loss Contingency Accrual | 10.8 |  |  | $ 13.0
Loss Contingency Accrual, Period Increase (Decrease) | $ 2.2 |  |  |

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