Quarterly report pursuant to Section 13 or 15(d)

COMMITMENTS AND CONTINGENCIES (Narrative) (Details)

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COMMITMENTS AND CONTINGENCIES (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Loss Contingencies [Line Items]      
Loss Contingency Accrual $ 5.0    
Loans to and accounts receivable from the Canadian Entities 50.4 $ 51.6 $ 51.6
Contingent claims 54.3 $ 55.6 $ 55.6
Michigan Electricity Matters [Member]      
Loss Contingencies [Line Items]      
Loss Contingency Accrual $ 13.0