DERIVATIVES AND HEDGING ACTIVITIES - Narrative (Details) - Designated as Hedging Instrument - Interest Rate Swap - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Closed portfolio loans used in hedging relationship	$ 2,400,000,000	$ 2,500,000,000
Cumulative amount of last-of-layer fair value hedging basis adjustments	17,750,000	$ (405,000)
Fair Value Hedging
Derivative [Line Items]
Term of contract		2 years
Notional amounts	1,000,000,000	$ 1,000,000,000
Net effect on interest income	(390,000)
Carrying amount of the last-of-layer hedged assets	1,017,750,000	999,595,000
Cash collateral	$ 18,200,000	$ 2,800,000