DERIVATIVE INSTRUMENTS - Offsetting of Financial Liabilities and Derivative Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	$ (285)	$ (346)
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	(285)	(346)
Financial instruments, amounts not offset	152	82
Derivative, collateral, right to reclaim securities	37	245
Derivative, collateral, right to reclaim cash	68	10
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	(28)	(9)
Derivative liability, not subject to master netting arrangement	(102)	(128)
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	(102)	(128)
Derivative liability, fair value, gross liability including not subject to master netting arrangement	(387)	(474)
Net amount of derivative liabilities presented in balance sheet	(387)	(474)
Derivative liability, fair value, amount offset against collateral	(130)	(137)
Gross amounts of recognized financial instruments, offsetting liabilities	(1,439)	(1,080)
Gross amounts offset in statement of financial position, offsetting liabilities	0	0
Net amounts of financial instruments presented in balance sheet, offsetting liabilities	(1,439)	(1,080)
Carrying value of financial instruments, liabilities not offset in balance sheet	1,181	674
Securities collateral, liabilities not offset in balance sheet	37	245
Cash collateral, liabilities not offset in balance sheet	68	10
Financial instruments, amount of liabilities offset against collateral	(153)	(151)
Over the Counter - Bilateral
Offsetting Liabilities [Line Items]
Gross amount of recognized derivative liabilities	(285)	(346)
Gross amount of assets offset in balance sheet	0	0
Derivative liability, fair value, amount not offset against collateral	(285)	(346)
Financial instruments, amounts not offset	152	82
Derivative, collateral, right to reclaim securities	37	245
Derivative, collateral, right to reclaim cash	68	10
Derivative liability, fair value, amount offset against collateral, subject to master netting agreement	(28)	(9)
Derivative liability, not subject to master netting arrangement	(102)	(128)
Derivative liability, fair value, amount offset against collateral, not subject to master netting agreement	(102)	(128)
Securities Lending and Similar Arrangements
Offsetting Liabilities [Line Items]
Gross amounts of recognized financial instruments, offsetting liabilities	(1,052)	(606)
Gross amounts offset in statement of financial position, offsetting liabilities	0	0
Net amounts of financial instruments presented in balance sheet, offsetting liabilities	(1,052)	(606)
Carrying value of financial instruments, liabilities not offset in balance sheet	1,029	592
Securities collateral, liabilities not offset in balance sheet	0	0
Cash collateral, liabilities not offset in balance sheet	0	0
Financial instruments, amount of liabilities offset against collateral	$ (23)	$ (14)