FAIR VALUE MEASUREMENTS - Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 35.3	$ 118.1	$ 45.8	$ 91.4
Included in earnings	29.5	(6.5)	43.3	83.1
Settlements	(3.4)	(38.8)	(27.7)	(101.7)
Ending balance	61.4	72.8	61.4	72.8
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on assets still held at the reporting date	27.8	(6.5)	40.4	81.8
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0.0	0.0	(1.1)	0.0
Included in earnings	(0.3)	(34.4)	(0.9)	(39.7)
Settlements	0.0	4.2	1.7	9.5
Ending balance	(0.3)	(30.2)	(0.3)	(30.2)
Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date	$ (0.3)	$ (30.2)	$ (0.3)	$ (30.2)