DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 383	$ 313
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	383	313
Financial instruments, amount not offset	(229)	(190)
Derivative, collateral, obligation to return securities	(7)	(7)
Derivative, collateral, obligation to return cash	(132)	(113)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	15	3
Derivative asset, not subject to master netting arrangement	89	169
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	89	169
Derivative asset, fair value, gross asset including not subject to master netting arrangement	472	482
Net amount of derivative assets presented in balance sheet	472	482
Derivative asset, fair value, amount offset against collateral	104	172
Gross amounts of recognized financial instruments	3,424	2,342
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	3,424	2,342
Carrying value of financial instruments not offset in balance sheet	(229)	(190)
Securities collateral, not offset in balance sheet	(7)	(7)
Cash collateral, not offset in balance sheet	(3,084)	(1,973)
Financial instruments, amount of assets offset against collateral	104	172
Over the Counter - Bilateral
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	362	310
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	362	310
Financial instruments, amount not offset	(229)	(190)
Derivative, collateral, obligation to return securities	(7)	(7)
Derivative, collateral, obligation to return cash	(121)	(113)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	5	0
Derivative asset, not subject to master netting arrangement	89	169
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	89	169
Other the Counter - Cleared
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	21	3
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	21	3
Financial instruments, amount not offset	0	0
Derivative, collateral, obligation to return securities	0	0
Derivative, collateral, obligation to return cash	(11)	0
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	10	3
Securities Lending and Similar Arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	2,952	1,860
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	2,952	1,860
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	(2,952)	(1,860)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0