DERIVATIVE INSTRUMENTS - Offsetting of Financial Liabilities and Derivative Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	$ 488	$ 460
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	488	460
Financial instruments, amount not offset	(229)	(190)
Derivative, collateral, right to reclaim securities	(175)	(222)
Derivative, collateral, right to reclaim cash	(2)	(33)
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	82	15
Derivative liability, not subject to master netting arrangement	235	126
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	235	126
Derivative liability, fair value, gross liability including not subject to master netting arrangement	723	586
Net amount of derivative liabilities presented in balance sheet	723	586
Derivative liability, fair value, amount offset against collateral	317	141
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	3,692	2,462
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	3,692	2,462
Carrying value of financial instruments, liabilities not offset in balance sheet	(3,181)	(2,050)
Securities Collateral, Liabilities Not Offset in Balance Sheet	(175)	(222)
Cash Collateral, Liabilities Not Offset in Balance Sheet	(2)	(33)
Financial instruments, amount of liabilities offset against collateral	334	157
Over the Counter - Bilateral
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	488	459
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	488	459
Financial instruments, amount not offset	(229)	(190)
Derivative, collateral, right to reclaim securities	(175)	(222)
Derivative, collateral, right to reclaim cash	(2)	(32)
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	82	15
Derivative liability, not subject to master netting arrangement	235	126
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	235	126
Exchange Cleared [Member]
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities		1
Gross amount of assets offset in balance sheet		0
Derivative liability, fair value, amount not offset against collateral		1
Financial instruments, amount not offset		0
Derivative, collateral, right to reclaim securities		0
Derivative, collateral, right to reclaim cash		(1)
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement		0
Securities Lending and Similar Arrangements
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	2,969	1,876
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	2,969	1,876
Carrying value of financial instruments, liabilities not offset in balance sheet	(2,952)	(1,860)
Securities Collateral, Liabilities Not Offset in Balance Sheet	0	0
Cash Collateral, Liabilities Not Offset in Balance Sheet	0	0
Financial instruments, amount of liabilities offset against collateral	$ 17	$ 16