RELATED PARTIES - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Proceeds from note receivable held by variable interest entities	$ 362		$ 253
Payment of SPE liabilities		$ 302		$ 209	$ 0	$ 302	$ 209
Interest expense					443	378	375
Buyer-sponsored SPEs
Related Party Transaction [Line Items]
Interest income						22	34
Interest expense					$ 0	$ 12	$ 29
Weighted average interest rate on SPE financial investments					5.50%	5.50%	5.50%
Monetization SPEs
Related Party Transaction [Line Items]
Weighted average interest rate on SPE long-term notes						5.60%	5.60%