OPERATING REVENUES - OTHER OPERATING REVENUES (Details) - Other operating revenues - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Operating Revenues
Other operating revenues	$ 26.3	$ (1.1)	$ 27.2	$ (4.6)
Alternative revenues
Disaggregation of Operating Revenues
Other operating revenues	1.1	(14.2)	(18.6)	(30.3)
Late payment charges
Disaggregation of Operating Revenues
Other operating revenues	12.0	11.1	25.2	22.5
Rental revenues
Disaggregation of Operating Revenues
Other operating revenues	$ 13.2	$ 2.0	$ 20.6	$ 3.2