COMMITMENTS AND CONTINGENT LIABILITIES - Funding Agreements (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Federal Home Loan Bank (FHLB)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	$ 6,900
Issued During the Period	34,298
Repaid During the Period	34,358
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	6,840
Difference related to remaining amortization	8	$ 9
Funding Agreement-Backed Notes Program (FABN)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	0
Issued During the Period	1,150
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	1,150
Difference related to remaining amortization	7
Short-Term Funding Agreements Maturing in Less than One Year | Federal Home Loan Bank (FHLB)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	4,608
Issued During the Period	34,298
Repaid During the Period	34,358
Long-term Agreements Maturing Within One Year	490
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	5,038
Short-Term Funding Agreements Maturing in Less than One Year | Funding Agreement-Backed Notes Program (FABN)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	0
Issued During the Period	0
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	0
Long-Term Funding Agreements Maturing Between Two and Five Years | Federal Home Loan Bank (FHLB)
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 Years	112
Outstanding Balance, period end	1,268
Long-Term Funding Agreements Maturing Between Two and Five Years | Funding Agreement-Backed Notes Program (FABN)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	0
Issued During the Period	650
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	650
Long-Term Funding Agreements Maturing in Greater than Five Years | Federal Home Loan Bank (FHLB)
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 Years	(112)
Outstanding Balance, period end	534
Long-Term Funding Agreements Maturing in Greater than Five Years | Funding Agreement-Backed Notes Program (FABN)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	0
Issued During the Period	500
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	500
Long-Term Funding Agreements | Federal Home Loan Bank (FHLB)
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 Years	0
Outstanding Balance, period end	1,802
Long-Term Funding Agreements | Funding Agreement-Backed Notes Program (FABN)
Restructuring Reserve [Roll Forward]
Outstanding Balance, period start	0
Issued During the Period	1,150
Repaid During the Period	0
Long-term Agreements Maturing Within One Year	0
Long-term Agreements Maturing Within Five Years	0
Outstanding Balance, period end	$ 1,150