DERIVATIVE INSTRUMENTS - BALANCE SHEET OFFSETTING (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Cash collateral
Cash collateral in margin account	$ 3.0	$ 2.7
Cash collateral received in margin account		0.2
Offsetting Derivative Assets
Gross amount recognized on the balance sheet	10.3	15.9
Gross amount not offset on the balance sheet	(0.9)	(4.0)
Net amount	9.4	11.9
Collateral received		0.2
Offsetting Derivative Liabilities
Gross amount recognized on the balance sheet	4.7	7.9
Gross amount not offset on the balance sheet	(0.9)	(4.9)
Net amount	$ 3.8	3.0
Collateral posted		$ 1.1

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