FAIR VALUE (Fair Value Measurements, Non-recurring) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 72,900	$ 102,000
LHFS	241,300	289,000
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets	49,358	68,248
Vehicle inventory	294,156	346,265
LHFS	5,198,114	1,131,214
MSRs	7,318	8,197
Nonrecurring | Lower-of-cost-or fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
LHFS	2,600,000
Nonrecurring | Impaired commercial LHFI
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	185,261	489,860
Total carrying value of the loans	175,800	448,800
Nonrecurring | Auto loans impaired due to bankruptcy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	187,837	201,007
Goodwill	350,000	0
Nonrecurring | Impaired personal loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
LHFS	808,400	1,000,000
Nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets	0	0
Vehicle inventory	0	0
LHFS	0	0
MSRs	0	0
Nonrecurring | Level 1 | Impaired commercial LHFI
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Nonrecurring | Level 1 | Auto loans impaired due to bankruptcy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Goodwill	0	0
Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets	8,693	17,168
Vehicle inventory	294,156	346,265
LHFS	103	0
MSRs	0	0
Nonrecurring | Level 2 | Impaired commercial LHFI
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	52,195	133,640
Nonrecurring | Level 2 | Auto loans impaired due to bankruptcy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	187,837	200,504
Goodwill	0	0
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets	40,665	51,080
Vehicle inventory	0	0
LHFS	5,198,011	1,131,214
MSRs	7,318	8,197
Nonrecurring | Level 3 | Impaired commercial LHFI
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	133,066	356,220
Nonrecurring | Level 3 | Auto loans impaired due to bankruptcy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	503
Goodwill	$ 350,000	$ 0