INVESTMENTS - Schedule of Unrealized Losses on Debt Securities (Details) $ in Millions	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 1,632.5
Gross unrealized losses, less than 12 months	(11.9)
Fair value, 12 months or greater	0.0
Gross unrealized losses, 12 months or greater	0.0
Total fair value	1,632.5
Total gross unrealized losses	(11.9)
United States government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	85.1
Gross unrealized losses, less than 12 months	(0.7)
Fair value, 12 months or greater	0.0
Gross unrealized losses, 12 months or greater	0.0
Total fair value	85.1
Total gross unrealized losses	(0.7)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	433.3
Gross unrealized losses, less than 12 months	(2.9)
Fair value, 12 months or greater	0.0
Gross unrealized losses, 12 months or greater	0.0
Total fair value	433.3
Total gross unrealized losses	(2.9)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	1,114.1
Gross unrealized losses, less than 12 months	(8.3)
Fair value, 12 months or greater	0.0
Gross unrealized losses, 12 months or greater	0.0
Total fair value	1,114.1
Total gross unrealized losses	$ (8.3)

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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