DERIVATIVE INSTRUMENTS - Fair Value and Notional Amount of Derivatives with Counterparty Credit Risk (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	$ 25,751	$ 43,927
Asset Derivatives Fair Value	331	1,207
Liability Derivatives Fair Value	(474)	(1,998)
AA
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	4,708	6,844
Asset Derivatives Fair Value	52	247
Liability Derivatives Fair Value	(37)	(308)
A
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	20,604	36,019
Asset Derivatives Fair Value	271	900
Liability Derivatives Fair Value	(370)	(1,621)
BBB
Fair Value and Notional Amount of Derivatives with Counterparty Credit RIsk [Line Items]
Notional Amount of Derivatives	439	1,064
Asset Derivatives Fair Value	8	60
Liability Derivatives Fair Value	$ (67)	$ (69)