FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements on a Nonrecurring Basis (Details) - Nonrecurring measurement basis - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	$ 55	$ 60
MSRs	165	178
Foreclosed assets	46	42
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	0	0
MSRs	0	0
Foreclosed assets	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	55	60
MSRs	0	0
Foreclosed assets	46	42
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	0	0
MSRs	165	178
Foreclosed assets	$ 0	$ 0