DERIVATIVES - Effect of Derivative Instruments on Net Income and Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pre-tax net gains recognized in OCI	$ 129	$ 51
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	5	(20)
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of pretax net gains (losses) from OCI into income statement	$ (1)	$ 0