ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Performance Indicators for Nonperforming Assets (Details)	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	0.59%	0.66%
Nonperforming assets as a percentage of total assets	0.45%	0.50%
Commercial
Financing Receivable, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	0.21%	0.17%
Nonperforming assets as a percentage of total assets	0.15%	0.13%
Retail
Financing Receivable, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	0.38%	0.49%
Nonperforming assets as a percentage of total assets	0.30%	0.37%