SEGMENT INFORMATION - Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment information
Stock-based compensation expense	$ 19.5	$ 16.0	$ 53.0	$ 46.9
Corporate and unallocated
Segment information
Payroll costs	61.7	50.1	173.5	151.0
Stock-based compensation expense	19.2	16.0	52.7	46.9
Professional service expenses	16.7	13.3	50.1	49.2
Other operating expenses	$ 11.6	$ 11.1	$ 35.5	$ 35.3