FAIR VALUE MEASUREMENTS - Schedule of Gain (Loss) on Assets and Liabilities Measured on Nonrecurring Basis Included in Earnings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Nonrecurring measurement basis | Collateral-dependent loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) included in earnings on assets measured on a nonrecurring basis	$ (21)	$ (8)	$ (65)	$ (36)