DERIVATIVES - Effect of Derivative Instruments on Net Income and Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net (losses) gains recognized in OCI	$ 0	$ (5)	$ 118	$ 138
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	68	(22)	128	(62)
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	$ (11)	$ 8	$ (22)	$ 9