ALLOWANCE FOR CREDIT LOSSES - Schedule of Allowance for Credit Losses for Other Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 54		$ 0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	48		44
Total provision for credit losses	48	$ 0	44	$ 0
Other, net	0		32
Allowance for credit losses at end of period	102		102
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	8		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	10		4
Total provision for credit losses	10		4
Other, net	0		0
Allowance for credit losses at end of period	18		18
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	5		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	2		5
Total provision for credit losses	2		5
Other, net	0		0
Allowance for credit losses at end of period	7		7
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	41		0
Net credit losses (NCLs)	0		0
Net reserve builds (releases)	36		42
Total provision for credit losses	36		42
Other, net	0		32
Allowance for credit losses at end of period	$ 77		77
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