DESCRIPTION OF BUSINESS AND ACCOUNTING POLICIES - Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	$ 0.7	$ 0.0	$ 4.2	$ 1.8
Technology and development
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	0.7		3.2	0.9
General and administrative
Finite-Lived Intangible Assets [Line Items]
Impairment of long-lived assets held-for-use	$ 0.0		$ 1.0	$ 0.9