DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 703	$ 450
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	703	450
Financial instruments, amount not offset	(387)	(295)
Derivative, collateral, obligation to return securities	(5)	(73)
Derivative, collateral, obligation to return cash	(250)	(76)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	61	6
Derivative asset, not subject to master netting arrangement	138	133
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	138	133
Derivative asset, fair value, gross asset including not subject to master netting arrangement	841	583
Net amount of derivative assets presented in balance sheet	841	583
Derivative asset, fair value, amount offset against collateral	199	139
Gross amounts of recognized financial instruments	2,701	1,523
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	2,701	1,523
Carrying value of financial instruments not offset in balance sheet	(387)	(295)
Securities collateral, not offset in balance sheet	(5)	(73)
Cash collateral, not offset in balance sheet	(2,110)	(1,016)
Financial instruments, amount of assets offset against collateral	199	139
Over the Counter - Bilateral
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	703	450
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	703	450
Financial instruments, amount not offset	(387)	(295)
Derivative, collateral, obligation to return securities	(5)	(73)
Derivative, collateral, obligation to return cash	(250)	(76)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	61	6
Derivative asset, not subject to master netting arrangement	138	133
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	138	133
Securities Lending and Similar Arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	1,860	940
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	1,860	940
Carrying value of financial instruments not offset in balance sheet	0	0
Securities collateral, not offset in balance sheet	0	0
Cash collateral, not offset in balance sheet	(1,860)	(940)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0