SUPPLEMENTAL CASH FLOW INFORMATION - RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Additional Cash Flow Elements and Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 48.1	$ 38.9	$ 45.7
Restricted cash included in other current assets	0.0		0.8
Restricted cash included in other long term assets	23.6		26.9
Cash, cash equivalents, and restricted cash	$ 71.7	$ 58.6	$ 73.4	$ 72.7	$ 168.8	$ 61.9