SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - LOANS (Details)	12 Months Ended
	Dec. 31, 2017
Loans disclosures
Delinquency period for interest income on mortgage and commercial loans to be discontinued	80 days
Period for non-accrual loans and loans past due still on accrual evaluated for impairment	80 days
Minimum performance period for loans to be returned to accrual status	6 months
Period in which loans were classified as PCI loans	90 days
Period for valuation of commercial-related credits	1 year
Minimum
Loans disclosures
Selling cost for collateral dependent loans expressed as a percentage of fair value of the underlying collateral	10.00%
Maximum
Loans disclosures
Selling cost for collateral dependent loans expressed as a percentage of fair value of the underlying collateral	13.00%
Consumer: Credit cards | Maximum
Loans disclosures
Period for past due loans for updating collateral values	120 days
Residential mortgage loans and home equity loans | Minimum
Loans disclosures
Period for past due loans for updating collateral values	90 days
Residential mortgage loans and home equity loans | Maximum
Loans disclosures
Period for past due loans for updating collateral values	180 days