ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses for AFS Debt Securities (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		$ 8		$ 0
Less: Write-offs		0		0
Recoveries of amounts written-off		1		1
Net credit losses (NCLs)		1		1
Credit losses on securities without previous credit losses		0		8
Net reserve builds (releases) on securities with previous credit losses		(3)		(3)
Total provision for credit losses	[1]	(4)	$ 0	4	$ 0
Initial allowance on purchased credit deteriorated assets		0		0
Allowance for credit losses at end of period		5		5
Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period				0
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		3		0
Less: Write-offs		0		0
Recoveries of amounts written-off		0		0
Net credit losses (NCLs)		0		0
Credit losses on securities without previous credit losses		0		3
Net reserve builds (releases) on securities with previous credit losses		(3)		(3)
Total provision for credit losses		(3)		0
Initial allowance on purchased credit deteriorated assets		0		0
Allowance for credit losses at end of period		0		0
Foreign government | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period				0
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		5		0
Less: Write-offs		0		0
Recoveries of amounts written-off		1		1
Net credit losses (NCLs)		1		1
Credit losses on securities without previous credit losses		0		5
Net reserve builds (releases) on securities with previous credit losses		0		0
Total provision for credit losses		(1)		4
Initial allowance on purchased credit deteriorated assets		0		0
Allowance for credit losses at end of period		$ 5		5
Corporate | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period				$ 0

[1] In accordance with ASC 326.