COMMITMENTS AND CONTINGENT LIABILITIES - Funding Agreements with FHBLNY (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	$ 6,900
Issued During the Period	22,950
Repaid During the Period	23,158
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Year	0
Outstanding Balance, period end	6,692
Difference related to remaining amortization	8	$ 9
Federal Home Loan Bank of New York Short-Term Funding Agreements Maturing in One Year or Less
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	4,608
Issued During the Period	22,950
Repaid During the Period	23,158
Long-term Agreements Maturing Within One Year	490
Long-term Agreements Maturing Within Five Year	0
Outstanding Balance, period end	4,890
Federal Home Loan Bank of New York Long-Term Funding Agreements Maturing Between Two and Five Years
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	1,646
Issued During the Period	0
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	(490)
Long-term Agreements Maturing Within Five Year	112
Outstanding Balance, period end	1,268
Federal Home Loan Bank of New York Long-Term Funding Agreements Maturing in Greater than Five Years
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	646
Issued During the Period	0
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Year	(112)
Outstanding Balance, period end	534
Federal Home Loan Bank of New York Long-Term Funding Agreements
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	2,292
Issued During the Period	0
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	(490)
Long-term Agreements Maturing Within Five Year	0
Outstanding Balance, period end	$ 1,802