INVESTMENTS - Schedule of Investments in Continuous Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Fair value, less than twelve months		$ 154.8
Gross unrealized losses, less than twelve months		(0.2)
Fair value, twelve months or greater		0.0
Gross unrealized losses, twelve months or greater		0.0
Fair value, total		154.8
Gross unrealized losses, total		(0.2)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than twelve months		73.4
Gross unrealized losses, less than twelve months		(0.1)
Fair value, twelve months or greater		0.0
Gross unrealized losses, twelve months or greater		0.0
Fair value, total		73.4
Gross unrealized losses, total		(0.1)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than twelve months	$ 28.5	81.4
Gross unrealized losses, less than twelve months	(0.1)	(0.1)
Fair value, twelve months or greater	0.0	0.0
Gross unrealized losses, twelve months or greater	0.0	0.0
Fair value, total	28.5	81.4
Gross unrealized losses, total	$ (0.1)	$ (0.1)