DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 556	$ 180
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in the balance sheet	556	180
Financial instruments, amount not offset	(116)	(82)
Derivative, collateral, obligation to return securities	(343)	0
Derivative, collateral, obligation to return cash	(67)	(98)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	30	0
Derivative asset, not subject to master netting arrangement	241	151
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	241	151
Derivative asset, fair value, gross asset including not subject to master netting arrangement	797	331
Net amount of derivative assets presented in balance sheet	797	331
Derivative asset, fair value, amount offset against collateral	271	151
Gross amounts of recognized financial instruments	6,046	923
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	6,046	923
Carrying value of financial instruments not offset in balance sheet	(116)	(82)
Securities collateral, not offset in balance sheet	(343)	0
Cash collateral, not offset in balance sheet	(5,316)	(690)
Financial instruments, amount of assets offset against collateral	271	151
Securities lending and similar arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	5,249	592
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	5,249	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	(5,249)	(592)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0