NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loans held for investment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Troubled Debt Restructurings Sustained Performance Period	6 months
Loan value deliquency threshold to be valued at fair value, percent	60.00%
Nonacrual Sustained Performance Period	6 months
Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Individually Evaluated for Impairment	$ 1
Boat Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Individually Evaluated for Impairment	$ 1
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Delinquent	2 months
Residential Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Nonperforming	2 months 29 days
Residential Portfolio Segment [Member] | Loans Insured or Guaranteed by US Government Authorities [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Guaranteed Loans Past Due	2 months 29 days
Period Of Guaranteed Residential Mortgage Loans That Are No Longer Accruing Interest	1 year 3 months
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Nonperforming	2 months 29 days
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Delinquent	2 months
Financing Receivable, Individually Evaluated for Impairment	$ 1
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Delinquent	30 days
Financing Receivable, Individually Evaluated for Impairment	$ 1
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Delinquent	2 months
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due Of Financing Receivables To Be Considered Nonperforming	2 months 29 days
Threshold Period Past Due Of Financing Receivables To Be Considered Delinquent	30 days
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due for Write-off of Financing Receivable	3 months 28 days
Consumer Portfolio Segment [Member] | Personal Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due for Write-off of Financing Receivable	3 months 28 days
Consumer Portfolio Segment [Member] | Small Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due for Write-off of Financing Receivable	5 months 27 days
Consumer Portfolio Segment [Member] | Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due for Write-off of Financing Receivable	5 months 27 days	5 months 27 days
Finance Leases Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold Period Past Due for Write-off of Financing Receivable	3 months 28 days