CONTINGENTLY REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Shares issued (in shares)	1,000,000
Shares exchanged, value	$ 1	$ 2	$ 1
Common stock issued (in shares)	101,518,666				101,518,666		101,327,571
Common stock outstanding (in shares)	101,518,666	101,000,000	101,000,000	100,000,000	101,518,666	100,000,000	101,327,571	100,000,000	100,000,000	100,000,000
Shares issued (in shares)			72,000,000	161,000,000	71,913,170	161,394,452
Shares issued			$ 2,650	$ 2,500	$ 2,700	$ 2,500
Dividends					0		$ 0
Mezzanine equity	$ 7,900				$ 7,900		$ 5,200
Preferred stock, issued (in shares)	575,864,510				575,864,510
Shares outstanding (in shares)	575,864,510				575,864,510
Common Stock
Class of Stock [Line Items]
Shares issued (in shares)					321,304	0
Shares exchanged, value					$ 4