OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance				$ (374.0)	$ (374.0)	$ (102.7)	$ (33.6)
Net current period other comprehensive income	$ 0.0	$ 0.1	$ 6.7	(1.8)	5.0	0.6
Ending balance	1,032.4				1,032.4	(374.0)	(102.7)
Change in net unrealized gains on investment:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance				$ 0.6	0.6	0.0	0.0
Other comprehensive income before reclassifications					5.3	0.6	0.0
Realized gains on investments reclassified from AOCI to net income					(0.3)	0.0	0.0
Net current period other comprehensive income					5.0	0.6	0.0
Ending balance	$ 5.6				$ 5.6	$ 0.6	$ 0.0

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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