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	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
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	$ (19)	$ (5)
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	0	(5)
Foreclosed 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	(1)	(1)
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	$ 4	$ 0