DERIVATIVE INSTRUMENTS - Offsetting of Financial Liabilities and Derivative Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	$ 876	$ 466
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	876	466
Financial instruments, amount not offset	(387)	(295)
Derivative, collateral, right to reclaim securities	(447)	(43)
Derivative, collateral, right to reclaim cash	(12)	(69)
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	30	59
Derivative liability, not subject to master netting arrangement	218	231
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	218	231
Derivative liability, fair value, gross liability including not subject to master netting arrangement	1,094	697
Net amount of derivative liabilities presented in balance sheet	1,094	697
Derivative liability, fair value, amount offset against collateral	248	290
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	2,990	1,661
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	2,990	1,661
Carrying value of financial instruments, liabilities not offset in balance sheet	(2,247)	(1,235)
Securities Collateral, Liabilities Not Offset in Balance Sheet	(447)	(43)
Cash Collateral, Liabilities Not Offset in Balance Sheet	(12)	(69)
Financial instruments, amount of liabilities offset against collateral	284	314
Over the Counter - Bilateral
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	876	466
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	876	466
Financial instruments, amount not offset	(387)	(295)
Derivative, collateral, right to reclaim securities	(447)	(43)
Derivative, collateral, right to reclaim cash	(12)	(69)
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	30	59
Derivative liability, not subject to master netting arrangement	218	231
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	218	231
Securities Lending and Similar Arrangements
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Financial Instruments, Offsetting Liabilities	1,896	964
Gross Amounts Offset in Statement of Financial Position, Offsetting Liabilities	0	0
Net Amounts of Financial Instruments Presented in Balance Sheet, Offsetting Liabilities	1,896	964
Carrying value of financial instruments, liabilities not offset in balance sheet	(1,860)	(940)
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	$ 36	$ 24