LOANS (Loans by credit quality indicator narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Held to maturity	$ 10,050,456,000		$ 10,023,051,000
Allowance for credit loss	130,172,000	$ 97,350,000	$ 131,606,000	$ 70,395,000
Loans secured by residential real estate property in process of foreclosure	$ 1,600,000
Loans delinquent 30 to 89 days, percentage	0.16%		0.23%
Interest income on nonaccrual loans	$ 0	$ 0
Nonaccrual loans with no related allowance	30,500,000		$ 32,500,000
Nonpass | Paycheck Protection Program ("PPP")
Financing Receivable, Credit Quality Indicator [Line Items]
Held to maturity	84,100,000		$ 77,100,000
Allowance for credit loss	$ 0