DERIVATIVE INSTRUMENTS - Offsetting of Financial Assets and Derivative Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Gross amount of recognized derivative assets	$ 255	$ 180
Gross amount of liabilities offset in balance sheet	0	0
Net amount of derivative assets presented in the balance sheet	255	180
Financial instruments, amount not offset	(138)	(82)
Derivative, collateral, obligation to return securities	(32)	0
Derivative, collateral, obligation to return cash	(82)	(98)
Derivative asset, fair value, amount offset against collateral, subject to master netting agreement	3	0
Derivative asset, not subject to master netting arrangement	202	151
Derivative asset, fair value, amount offset against collateral, not subject to master netting agreement	202	151
Derivative asset, fair value, gross asset including not subject to master netting arrangement	457	331
Net amount of derivative assets presented in balance sheet	457	331
Derivative asset, fair value, amount offset against collateral	205	151
Gross amounts of recognized financial instruments	4,095	923
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	4,095	923
Carrying value of financial instruments not offset in balance sheet	(138)	(82)
Securities collateral, not offset in balance sheet	(32)	0
Cash collateral, not offset in balance sheet	(3,720)	(690)
Financial instruments, amount of assets offset against collateral	205	151
Securities lending and similar arrangements
Offsetting Assets [Line Items]
Gross amounts of recognized financial instruments	3,638	592
Gross amounts offset in balance sheet	0	0
Net amounts of assets presented in balance sheet	3,638	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	(3,638)	(592)
Financial instruments, amount of assets offset against collateral	$ 0	$ 0