INCOME TAXES - Reconciliation of Beginning and Ending Amount of Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Uncertain gross tax positions, beginning balance	$ 150.7	$ 225.6	$ 245.5
Current year tax positions	55.4	37.8	77.7
Increase in prior year tax positions	0.8	13.9	63.7
Decrease in prior year tax positions	(3.8)	(78.8)	(65.0)
Settlements	0.0	(46.5)	(95.3)
Lapse of statutes of limitations	0.0	(1.3)	(1.0)
Uncertain gross tax positions, ending balance	$ 203.1	$ 150.7	$ 225.6