INVESTMENTS - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Investment Income [Line Items]
Total					$ 8.1	$ 7.3	$ 5.9
Investment expense					(1.9)	(2.3)	(0.5)
Net investment income	$ 4.0	$ 0.9	$ 0.7	$ 0.6	6.2	5.0	5.4
Interest on bonds
Net Investment Income [Line Items]
Total					2.4	2.4	4.2
Interest on deposits and cash equivalents
Net Investment Income [Line Items]
Total					5.7	1.1	1.7
Other investments
Net Investment Income [Line Items]
Total					$ 0.0	$ 3.8	$ 0.0