DERIVATIVE INSTRUMENTS - Fair Value and Notional Amount of Derivatives with Counterparty Credit Risk (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount of Derivatives	$ 38,355	$ 25,751
Asset Derivatives Fair Value	417	331
Liability Derivatives Fair Value	(387)	(474)
AA
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount of Derivatives	5,399	4,708
Asset Derivatives Fair Value	63	52
Liability Derivatives Fair Value	(23)	(37)
A
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount of Derivatives	32,513	20,604
Asset Derivatives Fair Value	350	271
Liability Derivatives Fair Value	(311)	(370)
BBB
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount of Derivatives	443	439
Asset Derivatives Fair Value	4	8
Liability Derivatives Fair Value	$ (53)	$ (67)