LOAN SERVICING - Schedule of Mortgage Servicing Rights Activity (Details) - Mortgage Servicing Rights - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Servicing Assets at Fair Value [Line Items]
Mortgage loans sold with servicing retained	$ 6,429.0	$ 5,729.0
Mortgage loans sold with servicing retained	1,280.0	980.0	$ 1,056.0
Pre-tax net gains (losses) resulting from above loan sales	21.0	3.0	(12.0)
Mortgage servicing fees	15.0	14.0	13.0
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	59.5	52.8	44.4
Additions	16.6	11.3	13.0
Payoffs and curtailments	(3.4)	(2.2)	(4.4)
Impairment (charge) / recovery	0.1	(0.2)	2.5
Amortization / other	(2.3)	(2.2)	(2.7)
Balance at end of period	70.5	59.5	52.8
Fair value, beginning of period	71.8	68.6	46.0
Fair value, end of period	86.3	71.8	$ 68.6
Valuation allowance for servicing rights	$ 0.1	$ 0.2