EQUITY - Summary of Changes In Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 2,284	$ 2,079	$ 2,112	$ 2,517
Net transfers to Parent	(487)	(22)	(479)	(190)
Stockholders' Equity, Special Payment to Parent	(1,520)		(1,520)
Comprehensive income (loss)	(12)	34	152	(237)
Ending balance	265	2,091	265	2,091	$ 2,517
Accounting Standards Update [Extensible Enumeration]					Accounting Standards Update 2016-13 [Member]
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				1
Ending balance					$ 1
Parent Company Investment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	3,777	3,633	3,592	3,746
Net transfers to Parent	(457)	(22)	(449)	(190)
Stockholders' Equity, Special Payment to Parent	(1,520)		(1,520)
Comprehensive income (loss)	92	51	269	105
Ending balance	1,892	3,662	1,892	3,662	3,746
Parent Company Investment | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				1
Ending balance					1
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,493)	(1,554)	(1,480)	(1,229)
Net transfers to Parent	(30)	0	(30)	0
Stockholders' Equity, Special Payment to Parent	0		0
Comprehensive income (loss)	(104)	(17)	(117)	(342)
Ending balance	$ (1,627)	$ (1,571)	$ (1,627)	(1,571)	(1,229)
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 0
Ending balance					$ 0