ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses for Other Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	(4)
Total provision for credit losses	(4)	$ 0
Other, net	32
Allowance for credit losses at end of period	54
Cash and due from banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	(6)
Total provision for credit losses	(6)
Other, net	0
Allowance for credit losses at end of period	0
Deposits with banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	(6)
Total provision for credit losses	(6)
Other, net	0
Allowance for credit losses at end of period	8
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	0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	3
Total provision for credit losses	3
Other, net	0
Allowance for credit losses at end of period	5
Brokerage receivables
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	(1)
Total provision for credit losses	(1)
Other, net	0
Allowance for credit losses at end of period	0
All other assets
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0
Gross credit losses	0
Gross recoveries	0
Net credit losses (NCLs)	0
Net reserve builds (releases)	6
Total provision for credit losses	6
Other, net	32
Allowance for credit losses at end of period	41
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