INVESTMENTS IN AFFILIATES - Summary of Financial Information for Equity Method Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Current assets	$ 154.3	$ 107.1
Non-current assets	727.8	854.0
Total assets	882.1	961.1
Liabilities
Current liabilities	65.8	64.4
Non-current liabilities	175.0	200.7
Total liabilities	240.8	265.1
Income Statement
Operating revenue	489.3	471.7	$ 71.0
Operating costs and expenses	449.8	411.6	65.9
Operating income	39.5	60.1	5.1
Income from continuing operations	31.7	57.2	5.0
Net income	$ 31.7	$ 56.1	$ 5.0