INVESTMENTS - Schedule of Unrealized Losses on Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 353.9	$ 1,632.5
Gross unrealized losses, less than 12 months	(8.1)	(11.9)
Fair value, 12 months or greater	1,111.4	0.0
Gross unrealized losses, 12 months or greater	(60.0)	0.0
Total fair value	1,465.3	1,632.5
Total gross unrealized losses	(68.1)	(11.9)
United States government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	61.6	85.1
Gross unrealized losses, less than 12 months	(1.5)	(0.7)
Fair value, 12 months or greater	69.5	0.0
Gross unrealized losses, 12 months or greater	(4.6)	0.0
Total fair value	131.1	85.1
Total gross unrealized losses	(6.1)	(0.7)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	103.3	433.3
Gross unrealized losses, less than 12 months	(1.3)	(2.9)
Fair value, 12 months or greater	254.6	0.0
Gross unrealized losses, 12 months or greater	(12.7)	0.0
Total fair value	357.9	433.3
Total gross unrealized losses	(14.0)	(2.9)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	189.0	1,114.1
Gross unrealized losses, less than 12 months	(5.3)	(8.3)
Fair value, 12 months or greater	784.8	0.0
Gross unrealized losses, 12 months or greater	(42.5)	0.0
Total fair value	973.8	1,114.1
Total gross unrealized losses	(47.8)	$ (8.3)
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	2.5
Gross unrealized losses, 12 months or greater	(0.2)
Total fair value	2.5
Total gross unrealized losses	$ (0.2)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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