INVESTMENT SECURITIES - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) position	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) position	Sep. 30, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Percentage of debt securities considered to be of investment-grade	96.00%		96.00%
Maximum individual state general bond obligation as a percentage of total debt securities (percent)			1.00%
Securities in unrealized loss positions, number of positions	250		250
Securities, number of positions	1,530		1,530
Other-than-temporary impairments | $	$ 0.0	$ 0.0	$ 0.0	$ 0.0