INCOME TAXES - Schedule of Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Loss before income taxes	$ (147.4)	$ (297.7)	$ (521.1)
Amount
Statutory U.S. federal income tax benefit	(30.9)	(62.5)	(109.4)
Valuation allowance on deferred tax assets	34.9	65.8	116.7
Share-based compensation	5.5	4.9	(3.3)
Nondeductible compensation	1.2	1.3	1.8
Return to provision permanent adjustments	0.0	(3.5)	(0.5)
State net operating loss	(10.5)	(7.1)	(4.9)
Other	(0.2)	1.1	(0.4)
Total income tax expense (benefit)	$ 0.0	$ 0.0	$ 0.0
Percent
Statutory U.S. federal income tax benefit	21.00%	21.00%	21.00%
Valuation allowance on deferred tax assets	(23.70%)	(22.10%)	(22.40%)
Share-based compensation	(3.70%)	(1.60%)	0.60%
Nondeductible compensation	(0.80%)	(0.40%)	(0.30%)
Return to provision permanent adjustments	0.00%	1.20%	0.10%
State net operating loss	7.10%	2.40%	0.90%
Other	0.10%	(0.50%)	0.10%
Income tax expense (benefit)	0.00%	0.00%	0.00%