FAIR VALUE MEASUREMENTS - FAIR VALUE ACTIVITY (Details) - Significant unobservable inputs (Level 3) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Corporate securities
Assets:
Purchases	$ 2.3	$ 6.3	$ 7.8	$ 10.5
Sales	(1.9)	0.0	(10.7)	(1.4)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	0.4	6.3	(2.9)	9.1
Asset-backed securities
Assets:
Purchases	10.0	1.3	10.0	3.8
Sales	(10.1)	(0.2)	(10.4)	(7.7)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	(0.1)	1.1	(0.4)	(3.9)
Non-agency residential mortgage-backed securities
Assets:
Purchases				0.0
Sales				(0.1)
Issuances				0.0
Settlements				0.0
Purchases, sales, issuances and settlements, net		0.0		(0.1)
Total Fixed Maturities, Available For Sale
Assets:
Purchases	12.3	7.6	17.8	14.3
Sales	(12.0)	(0.2)	(21.1)	(9.2)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	0.3	7.4	(3.3)	5.1
Equity securities - corporate securities
Assets:
Purchases				0.0
Sales				(2.1)
Issuances				0.0
Settlements				0.0
Purchases, sales, issuances and settlements, net	0.0	0.0	0.0	(2.1)
Trading securities - commercial mortgage-backed securities
Assets:
Purchases, sales, issuances and settlements, net	0.0
Other invested assets - residual tranches
Assets:
Purchases	10.6	3.9	30.0	6.4
Sales	(1.0)	0.0	(5.3)	(0.3)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	$ 9.6	$ 3.9	$ 24.7	6.1
Collateralized loan obligations
Assets:
Purchases, sales, issuances and settlements, net				0.0
Trading securities - non-agency residential mortgage-backed securities
Assets:
Purchases, sales, issuances and settlements, net				$ 0.0

Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
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-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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