DERIVATIVES - Effect of Derivative Instruments on Net Income and Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net (losses) gains recognized in OCI	$ (11)	$ 91	$ 118	$ 143
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	55	(20)	60	(40)
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	$ (10)	$ 1	$ (11)	$ 1