ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses for AFS Debt Securities (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period		$ 0		$ 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		8		8
Total provision for credit losses	[1]	8	$ 0	8	$ 0
Initial allowance on purchased credit deteriorated assets		0		0
Allowance for credit losses at end of period		8		8
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		0		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		3		3
Total provision for credit losses		3		3
Initial allowance on purchased credit deteriorated assets		0		0
Allowance for credit losses at end of period		3		3
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		0		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		5		5
Total provision for credit losses		5		5
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.