FAIR VALUE OF ASSETS AND LIABILITIES - Reconciliation of Balance, Fair Value Measurement, Level 3 (Details) - Contingent Consideration Liability - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (3.4)	$ (29.3)	$ (18.6)	$ (60.2)
Purchases/acquisitions	0.0		(1.3)
Revision to purchase price allocation		0.0		5.5
Net unrealized gains and losses included in other gains and losses, net	0.0	(0.5)	4.7	10.9
Disposition/settlements	0.0	2.8	11.8	16.8
Ending balance	$ (3.4)	$ (27.0)	$ (3.4)	$ (27.0)