FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements on a Nonrecurring Basis (Details) - Nonrecurring measurement basis - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	$ 107	$ 102
MSRs	177	166
Foreclosed assets	36	40
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	107	102
MSRs	0	0
Foreclosed assets	36	40
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired collateral-dependent loans	0	0
MSRs	177	166
Foreclosed assets	$ 0	$ 0