FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements on a Nonrecurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Premises and equipment, net	$ 746	$ 761
Nonrecurring measurement basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent loans	426	312
Level 1 | Nonrecurring measurement basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent loans	0	0
Level 2 | Nonrecurring measurement basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent loans	426	312
Level 3 | Nonrecurring measurement basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral-dependent loans	$ 0	$ 0