INVESTMENTS - Schedule of Unrealized Losses on Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 8.4	$ 35.2
Gross unrealized losses, less than 12 months	(0.1)	(1.9)
Fair value, 12 months or greater	214.2	843.7
Gross unrealized losses, 12 months or greater	(5.2)	(25.6)
Total fair value	222.6	878.9
Total gross unrealized losses	(5.3)	(27.5)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0.0	0.0
Gross unrealized losses, less than 12 months	0.0	0.0
Fair value, 12 months or greater	19.9	67.1
Gross unrealized losses, 12 months or greater	(1.1)	(2.8)
Total fair value	19.9	67.1
Total gross unrealized losses	(1.1)	(2.8)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	8.4	10.2
Gross unrealized losses, less than 12 months	(0.1)	(1.8)
Fair value, 12 months or greater	53.3	172.7
Gross unrealized losses, 12 months or greater	(1.3)	(6.0)
Total fair value	61.7	182.9
Total gross unrealized losses	(1.4)	(7.8)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0.0	25.0
Gross unrealized losses, less than 12 months	0.0	(0.1)
Fair value, 12 months or greater	141.0	601.3
Gross unrealized losses, 12 months or greater	(2.8)	(16.6)
Total fair value	141.0	626.3
Total gross unrealized losses	$ (2.8)	(16.7)
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months		0.0
Gross unrealized losses, less than 12 months		0.0
Fair value, 12 months or greater		2.6
Gross unrealized losses, 12 months or greater		(0.2)
Total fair value		2.6
Total gross unrealized losses		$ (0.2)