NET LOSS PER SHARE - Antidilutive Securities (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive scurities	588	516	588	516
Stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive scurities	12	12	12	12
Contingently redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive scurities	576	504	576	504