ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses for Other Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 102		$ 0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	(13)		31
Total provision for credit losses	(13)	$ 0	31	$ 0
Other, net	(10)		22
Allowance for credit losses at end of period	79		79
Cash and due from banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	0		(6)
Total provision for credit losses	0		(6)
Other, net	0		0
Allowance for credit losses at end of period	0		0
Deposits with banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	18		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	7		11
Total provision for credit losses	7		11
Other, net	0		0
Allowance for credit losses at end of period	25		25
Securities borrowed and purchased under agreements to resell
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	7		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	(3)		2
Total provision for credit losses	(3)		2
Other, net	0		0
Allowance for credit losses at end of period	4		4
Brokerage receivables
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	0		(1)
Total provision for credit losses	0		(1)
Other, net	0		0
Allowance for credit losses at end of period	0		0
All other assets
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	77		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	(17)		25
Total provision for credit losses	(17)		25
Other, net	(10)		22
Allowance for credit losses at end of period	$ 50		50
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			26
Cumulative Effect, Period of Adoption, Adjustment | Cash and due from banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			6
Cumulative Effect, Period of Adoption, Adjustment | Deposits with banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			14
Cumulative Effect, Period of Adoption, Adjustment | Securities borrowed and purchased under agreements to resell
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			2
Cumulative Effect, Period of Adoption, Adjustment | Brokerage receivables
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			1
Cumulative Effect, Period of Adoption, Adjustment | All other assets
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period			$ 3