DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 234	$ 180
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	234	180
Financial instruments, amounts not offset	(152)	(82)
Derivative, collateral, obligation to return securities	(23)	0
Derivative, collateral, obligation to return cash	(58)	(98)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	1	0
Derivative asset, not subject to master netting arrangement	183	151
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	183	151
Derivative asset, fair value, gross asset including not subject to master netting arrangement	417	331
Net amounts of derivative assets presented in balance sheet	417	331
Derivative asset, fair value, amount offset against collateral	184	151
Gross amounts of recognized financial instruments	1,446	923
Gross amounts offest in balance sheet	0	0
Net amounts of assets presented in balance sheet	1,446	923
Carrying value of financial instruments not offset in balance sheet	(152)	(82)
Securities collateral, not offset in balance sheet	(23)	0
Cash collateral, not offset in balance sheet	(1,087)	(690)
Financial instruments, amount of assets offset against collateral	184	151
Over the Counter - Bilateral
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	231	180
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in balance sheet	231	180
Financial instruments, amounts not offset	(152)	(82)
Derivative, collateral, obligation to return securities	(23)	0
Derivative, collateral, obligation to return cash	(55)	(98)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	1	0
Derivative asset, not subject to master netting arrangement	183	151
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	183	151
Over the Counter- Cleared
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	3
Gross amount of liabilities offset in balance sheet	0
Net amount of derivative assets presented in balance sheet	3
Financial instruments, amounts not offset	0
Derivative, collateral, obligation to return securities	0
Derivative, collateral, obligation to return cash	(3)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	0
Securities Lending and Similar Arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	1,029	592
Gross amounts offest in balance sheet	0	0
Net amounts of assets presented in balance sheet	1,029	592
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	(1,029)	(592)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0