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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 63	$ 54	$ 55	$ 0
Gross credit losses	0	0	0	0
Gross recoveries	0	0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	(3)	48	6	44
Total provision for credit losses	(3)	48	6	44
Other, net	0	0	(1)	32
Allowance for credit losses at end of period	60	102	60	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	0	0
Gross credit losses	0	0	0	0
Gross recoveries	0	0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	0	0	0	(6)
Total provision for credit losses	0	0	0	(6)
Other, net	0	0	0	0
Allowance for credit losses at end of period	0	0	0	0
Deposits with banks
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	28	8	20	0
Gross credit losses	0	0	0	0
Gross recoveries		0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	(4)	10	5	4
Total provision for credit losses	(4)	10	5	4
Other, net	0	0	(1)	0
Allowance for credit losses at end of period	24	18	24	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	5	10	0
Gross credit losses	0	0	0	0
Gross recoveries	0	0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	3	2	(2)	5
Total provision for credit losses	3	2	(2)	5
Other, net	0	0	0	0
Allowance for credit losses at end of period	8	7	8	7
Brokerage receivables
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0	0	0	0
Gross credit losses	0	0	0	0
Gross recoveries	0	0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	0	0	0	(1)
Total provision for credit losses	0	0	0	(1)
Other, net	0	0	0	0
Allowance for credit losses at end of period	0	0	0	0
All other assets
Financing Receivable, Other Assets, Allowance For Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	30	41	25	0
Gross credit losses	0	0	0	0
Gross recoveries	0	0	0	0
Net credit losses (NCLs)	0	0	0	0
Net reserve builds (releases)	(2)	36	3	42
Total provision for credit losses	(2)	36	3	42
Other, net	0	0	0	32
Allowance for credit losses at end of period	$ 28	77	$ 28	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		0		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		0		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		0		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		0		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		0		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		$ 0		$ 3