FAIR VALUE MEASUREMENTS - Schedule of Gain (Loss) on Assets and Liabilities Measured on Nonrecurring Basis Included in Earnings (Details) - Nonrecurring measurement basis - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impaired 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	$ (34)	$ (13)	$ (35)
MSRs
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	(1)	3	2
Leased assets
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	$ (12)	$ (7)	$ (15)